Tag Archives: Android-Security

Android 14 introduces first-of-its-kind cellular connectivity security features

Posted by Roger Piqueras Jover, Yomna Nasser, and Sudhi Herle

Android is the first mobile operating system to introduce advanced cellular security mitigations for both consumers and enterprises. Android 14 introduces support for IT administrators to disable 2G support in their managed device fleet. Android 14 also introduces a feature that disables support for null-ciphered cellular connectivity.

Hardening network security on Android

The Android Security Model assumes that all networks are hostile to keep users safe from network packet injection, tampering, or eavesdropping on user traffic. Android does not rely on link-layer encryption to address this threat model. Instead, Android establishes that all network traffic should be end-to-end encrypted (E2EE).

When a user connects to cellular networks for their communications (data, voice, or SMS), due to the distinctive nature of cellular telephony, the link layer presents unique security and privacy challenges. False Base Stations (FBS) and Stingrays exploit weaknesses in cellular telephony standards to cause harm to users. Additionally, a smartphone cannot reliably know the legitimacy of the cellular base station before attempting to connect to it. Attackers exploit this in a number of ways, ranging from traffic interception and malware sideloading, to sophisticated dragnet surveillance.

Recognizing the far reaching implications of these attack vectors, especially for at-risk users, Android has prioritized hardening cellular telephony. We are tackling well-known insecurities such as the risk presented by 2G networks, the risk presented by null ciphers, other false base station (FBS) threats, and baseband hardening with our ecosystem partners.

2G and a history of inherent security risk

The mobile ecosystem is rapidly adopting 5G, the latest wireless standard for mobile, and many carriers have started to turn down 2G service. In the United States, for example, most major carriers have shut down 2G networks. However, all existing mobile devices still have support for 2G. As a result, when available, any mobile device will connect to a 2G network. This occurs automatically when 2G is the only network available, but this can also be remotely triggered in a malicious attack, silently inducing devices to downgrade to 2G-only connectivity and thus, ignoring any non-2G network. This behavior happens regardless of whether local operators have already sunset their 2G infrastructure.

2G networks, first implemented in 1991, do not provide the same level of security as subsequent mobile generations do. Most notably, 2G networks based on the Global System for Mobile Communications (GSM) standard lack mutual authentication, which enables trivial Person-in-the-Middle attacks. Moreover, since 2010, security researchers have demonstrated trivial over-the-air interception and decryption of 2G traffic.

The obsolete security of 2G networks, combined with the ability to silently downgrade the connectivity of a device from both 5G and 4G down to 2G, is the most common use of FBSs, IMSI catchers and Stingrays.

Stingrays are obscure yet very powerful surveillance and interception tools that have been leveraged in multiple scenarios, ranging from potentially sideloading Pegasus malware into journalist phones to a sophisticated phishing scheme that allegedly impacted hundreds of thousands of users with a single FBS. This Stingray-based fraud attack, which likely downgraded device’s connections to 2G to inject SMSishing payloads, has highlighted the risks of 2G connectivity.

To address this risk, Android 12 launched a new feature that enables users to disable 2G at the modem level. Pixel 6 was the first device to adopt this feature and it is now supported by all Android devices that conform to Radio HAL 1.6+. This feature was carefully designed to ensure that users are not impacted when making emergency calls.

Mitigating 2G security risks for enterprises

The industry acknowledged the significant security and privacy benefits and impact of this feature for at-risk users, and we recognized how critical disabling 2G could also be for our Android Enterprise customers.

Enterprises that use smartphones and tablets require strong security to safeguard sensitive data and Intellectual Property. Android Enterprise provides robust management controls for connectivity safety capabilities, including the ability to disable WiFi, Bluetooth, and even data signaling over USB. Starting in Android 14, enterprise customers and government agencies managing devices using Android Enterprise will be able to restrict a device’s ability to downgrade to 2G connectivity.

The 2G security enterprise control in Android 14 enables our customers to configure mobile connectivity according to their risk model, allowing them to protect their managed devices from 2G traffic interception, Person-in-the-Middle attacks, and other 2G-based threats. IT administrators can configure this protection as necessary, always keeping the 2G radio off or ensuring employees are protected when traveling to specific high-risk locations.

These new capabilities are part of the comprehensive set of 200+ management controls that Android provides IT administrators through Android Enterprise. Android Enterprise also provides comprehensive audit logging with over 80 events including these new management controls. Audit logs are a critical part of any organization's security and compliance strategy. They provide a detailed record of all activity on a system, which can be used to track down unauthorized access, identify security breaches, and troubleshoot system problems.

Also in Android 14

The upcoming Android release also tackles the risk of cellular null ciphers. Although all IP-based user traffic is protected and E2EE by the Android platform, cellular networks expose circuit-switched voice and SMS traffic. These two particular traffic types are strictly protected only by the cellular link layer cipher, which is fully controlled by the network without transparency to the user. In other words, the network decides whether traffic is encrypted and the user has no visibility into whether it is being encrypted.

Recent reports identified usage of null ciphers in commercial networks, which exposes user voice and SMS traffic (such as One-Time Password) to trivial over the air interception. Moreover, some commercial Stingrays provide functionality to trick devices into believing ciphering is not supported by the network, thus downgrading the connection to a null cipher and enabling traffic interception.

Android 14 introduces a user option to disable support, at the modem-level, for null-ciphered connections. Similarly to 2G controls, it’s still possible to place emergency calls over an unciphered connection. This functionality will greatly improve communication privacy for devices that adopt the latest radio hardware abstraction layer (HAL). We expect this new connectivity security feature to be available in more devices over the next few years as it is adopted by Android OEMs.

Continuing to partner to raise the industry bar for cellular security

Alongside our Android-specific work, the team is regularly involved in the development and improvement of cellular security standards. We actively participate in standards bodies such as GSMA Fraud and Security Group as well as the 3rd Generation Partnership Project (3GPP), particularly its security and privacy group (SA3). Our long-term goal is to render FBS threats obsolete.

In particular, Android security is leading a new initiative within GSMA’s Fraud and Security Group (FASG) to explore the feasibility of modern identity, trust and access control techniques that would enable radically hardening the security of telco networks.

Our efforts to harden cellular connectivity adopt Android’s defense-in-depth strategy. We regularly partner with other internal Google teams as well, including the Android Red Team and our Vulnerability Rewards Program.

Moreover, in alignment with Android’s openness in security, we actively partner with top academic groups in cellular security research. For example, in 2022 we funded via our Android Security and Privacy Research grant (ASPIRE) a project to develop a proof-of-concept to evaluate cellular connectivity hardening in smartphones. The academic team presented the outcome of that project in the last ACM Conference on Security and Privacy in Wireless and Mobile Networks.

The security journey continues

User security and privacy, which includes the safety of all user communications, is a priority on Android. With upcoming Android releases, we will continue to add more features to harden the platform against cellular security threats.

We look forward to discussing the future of telco network security with our ecosystem and industry partners and standardization bodies. We will also continue to partner with academic institutions to solve complex problems in network security. We see tremendous opportunities to curb FBS threats, and we are excited to work with the broader industry to solve them.

Special thanks to our colleagues who were instrumental in supporting our cellular network security efforts: Nataliya Stanetsky, Robert Greenwalt, Jayachandran C, Gil Cukierman, Dominik Maier, Alex Ross, Il-Sung Lee, Kevin Deus, Farzan Karimi, Xuan Xing, Wes Johnson, Thiébaud Weksteen, Pauline Anthonysamy, Liz Louis, Alex Johnston, Kholoud Mohamed, Pavel Grafov

An important step towards secure and interoperable messaging

Posted by Giles Hogben, Privacy Engineering Director

Most modern consumer messaging platforms (including Google Messages) support end-to-end encryption, but users today are limited to communicating with contacts who use the same platform. This is why Google is strongly supportive of regulatory efforts that require interoperability for large end-to-end messaging platforms.

For interoperability to succeed in practice, however, regulations must be combined with open, industry-vetted, standards, particularly in the area of privacy, security, and end-to-end encryption. Without robust standardization, the result will be a spaghetti of ad hoc middleware that could lower security standards to cater for the lowest common denominator and raise implementation costs, particularly for smaller providers. Lack of standardization would also make advanced features such as end-to-end encrypted group messaging impossible in practice – group messages would have to be encrypted and delivered multiple times to cater for every different protocol.

With the recent publication of the IETF’s Message Layer Security (MLS) specification RFC 9420, messaging users can look forward to this reality. For the first time, MLS enables practical interoperability across services and platforms, scaling to groups of thousands of multi-device users. It is also flexible enough to allow providers to address emerging threats to user privacy and security, such as quantum computing.

By ensuring a uniformly high security and privacy bar that users can trust, MLS will unleash a huge field of new opportunities for the users and developers of interoperable messaging services that adopt it. This is why we intend to build MLS into Google Messages and support its wide deployment across the industry by open sourcing our implementation in the Android codebase.

Moving Connected Device Security Standards Forward

Posted by Eugene Liderman, Director of Mobile Security Strategy, Google

As Mobile World Congress approaches, we have the opportunity to have deep and meaningful conversations across the industry about the present and future of connected device security. Ahead of the event, we wanted to take a moment to recognize and share additional details on the notable progress being made to form harmonized connected device security standards and certification initiatives that provide users with better transparency about how their sensitive data is protected.

Supporting the GSMA Working Party for Mobile Device Security Transparency

We’re pleased to support and participate in the recently announced GSMA working party, which will develop a first-of-its-kind smartphone security certification program. The program will leverage the Consumer Mobile Device Protection Profile (CMD PP) specification released by ETSI, a European Standards Development Organization (SDO), and will provide a consistent way to evaluate smartphones for critical capabilities like encryption, security updates, biometrics, networking, trusted hardware, and more.

This initiative should help address a significant gap in the market for consumers and policy makers, who will greatly benefit from a new, central security resource. Most importantly, these certification programs will evaluate connected devices across industry-accepted criteria. Widely-used devices, including smartphones and tablets, which currently do not have a familiar security benchmark or system in place, will be listed with key information on device protection capabilities to bring more transparency to users.

We hope this industry-run certification program can also benefit users and support policy makers in their work as they address baseline requirements and harmonization of standards.As policy makers consider changes through regulation and legislation, such as the UK’s Product Security and Telecommunications Infrastructure Act (PSTI), and emerging regulation like the EU Cyber Security and Cyber Resilience Acts, we share the concerns that today we are not equipped with globally recognized standards that are critical to increased security across the ecosystem. We join governments in the call to come together to ensure that we can build workable, harmonized standards to protect the security of users and mobile infrastructure today and build the resilience needed to protect our future.

The Importance of Harmonized Standards for Connected Devices

Connected devices, not just smartphones, are increasingly becoming the primary touchpoint for the most important aspects of our personal lives. From controlling the temperature of your home, to tracking your latest workout – connected devices have become embedded in our day-to-day tasks and activities. As consumers increasingly entrust more of their lives to their connected devices, they’re right to question the security protections provided and demand more transparency from manufacturers.

After we participated in a recent White House Workshop on IoT security labeling, we shared more about our commitment to security and transparency by announcing the extension of device security assessments – which started with Pixel 3 and now includes Nest, and Fitbit hardware. We have and always will strive to ensure our newly released products comply with the most prevalent security baselines that are defined by industry-recognized standards organizations. We will also remain transparent about critical security features – like how long our devices will receive security updates and our collaboration with security researchers that help us identify and fix security issues to help keep users safe.

By participating in international standards and certification programs such as our work as a member of the Connectivity Standards Alliance (Alliance), we’re working to raise the bar for the industry and develop a consistent set of security requirements that users can rely on.


New Research Continues to Help Inform Our Efforts to Establish Strong Security Standards and Labeling Practices

Last year, the Alliance formed the Product Security Working Group (PSWG). Over the past nine months, the working group has been making terrific progress on its mission to build an industry-run certification program for IoT devices that aligns with existing and future regulatory requirements to reduce fragmentation and promote harmonization.

Today, the Alliance in partnership with independent research firm Omdia, published a comprehensive research report that outlines all of the currently published and emerging global IoT security regulations and the standards baselines they map to. This critical research enables PSWG to hone its focus and efforts on harmonizing between ETSI EN 303 645 and NIST IR 8425, as these two baseline security standards were found to underpin the vast majority of the regulations outlined in the research report.

The other notable area of the report highlighted the need for transparent security labeling for connected devices, which has also become a very important industry initiative. A large majority (77%) of consumers surveyed indicated a device label that explains the privacy and security practices of the manufacturer would be important or very important to their purchasing decision. Transparent security labeling is critical in helping consumers understand which devices meet specific security standards and requirements during evaluation. We recently provided our principles for IoT security labeling and will continue to be a key contributor to efforts around providing users with transparent device security labels.

Creating Strong Connected Device Security Standards Together

It’s been inspiring to see all of the progress that the Connectivity Standards Alliance, GSMA and the industry at large has made on security standards and labeling initiatives in such a short time. It’s even more exciting to see how much collaboration there has been between both industry and the public sector on these efforts. We look forward to continuing the conversation and coordinating on these important security initiatives with policymakers, industry partners, developers and public interest advocates to bring more security and transparency to connected device users.

Vulnerability Reward Program: 2022 Year in Review

Posted by Sarah Jacobus, Vulnerability Rewards Team

It has been another incredible year for the Vulnerability Reward Programs (VRPs) at Google! Working with security researchers throughout 2022, we have been able to identify and fix over 2,900 security issues and continue to make our products more secure for our users around the world.

We are thrilled to see significant year over year growth for our VRPs, and have had yet another record breaking year for our programs! In 2022 we awarded over $12 million in bounty rewards – with researchers donating over $230,000 to a charity of their choice.

As in past years, we are sharing our 2022 Year in Review statistics across all of our programs. We would like to give a special thank you to all of our dedicated researchers for their continued work with our programs - we look forward to more collaboration in the future!

Android

The Android VRP had an incredible record breaking year in 2022 with $4.8 million in rewards and the highest paid report in Google VRP history of $605,000!

In our continued effort to ensure the security of Google device users, we have expanded the scope of Android and Google Devices in our program and are now incentivizing vulnerability research in the latest versions of Google Nest and Fitbit! For more information on the latest program version and qualifying vulnerability reports, please visit our public rules page.

We are also excited to share that the invite-only Android Chipset Security Reward Program (ACSRP) - a private vulnerability reward program offered by Google in collaboration with manufacturers of Android chipsets - rewarded $486,000 in 2022 and received over 700 valid security reports.

We would like to give a special shoutout to some of our top researchers, whose continued hard work helps to keep Android safe and secure:

  • Submitting an impressive 200+ vulnerabilities to the Android VRP this year, Aman Pandey of Bugsmirror remains one of our program’s top researchers. Since submitting their first report in 2019, Aman has reported more than 500 vulnerabilities to the program. Their hard work helps ensure the safety of our users; a huge thank you for all of their hard work!
  • Zinuo Han of OPPO Amber Security Lab quickly rose through our program’s ranks, becoming one of our top researchers. In the last year they have identified 150 valid vulnerabilities in Android.
  • Finding yet another critical exploit chain, gzobqq submitted our highest valued exploit to date.
  • Yu-Cheng Lin (林禹成) (@AndroBugs) remains one of our top researchers submitting just under 100 reports this year.

Chrome

Chrome VRP had another unparalleled year, receiving 470 valid and unique security bug reports, resulting in a total of $4 million of VRP rewards. Of the $4M, $3.5 million was rewarded to researchers for 363 reports of security bugs in Chrome Browser and nearly $500,000 was rewarded for 110 reports of security bugs in ChromeOS.

This year, Chrome VRP re-evaluated and refactored the Chrome VRP reward amounts to increase the reward amounts for the most exploitable and harmful classes and types of security bugs, as well as added a new category for memory corruption bugs in highly privileged processes, such as the GPU and network process, to incentivize research in these critical areas. The Chrome VRP increased the fuzzer bonuses for reports from VRP-submitted fuzzers running on the Google ClusterFuzz infrastructure as part of the Chrome Fuzzing program. A new bisect bonus was introduced for bisections performed as part of the bug report submission, which helps the security team with our triage and bug reproduction.

2023 will be the year of experimentation in the Chrome VRP! Please keep a lookout for announcements of experiments and potential bonus opportunities for Chrome Browser and ChromeOS security bugs.

The entire Chrome team sincerely appreciates the contributions of all our researchers in 2022 who helped keep Chrome Browser, ChromeOS, and all the browsers and software based on Chromium secure for billions of users across the globe.

In addition to posting about our Top 0-22 Researchers in 2022, Chrome VRP would like to specifically acknowledge some specific researcher achievements made in 2022:

  • Rory McNamara, a six-year participant in Chrome VRP as a ChromeOS researcher, became the highest rewarded researcher of all time in the Chrome VRP. Most impressive is that Rory has achieved this in a total of only 40 security bug submissions, demonstrating just how impactful his findings have been - from ChromeOS persistent root command execution, resulting in a $75,000 reward back in 2018, to his many reports of root privilege escalation both with and without persistence. Rory was also kind enough to speak at the Chrome Security Summit in 2022 to share his experiences participating in the Chrome VRP over the years. Thank you, Rory!
  • SeongHwan Park (SeHwa), a participant in the Chrome VRP since mid-2021, has been an amazing contributor of ANGLE / GPU security bug reports in 2022 with 11 solid quality reports of GPU bugs earning them a spot on Chrome VRP 2022 top researchers list. Thank you, SeHwa!

Securing Open Source

Recognizing the fact that Google is one of the largest contributors and users of open source in the world, in August 2022 we launched OSS VRP to reward vulnerabilities in Google's open source projects - covering supply chain issues of our packages, and vulnerabilities that may occur in end products using our OSS. Since then, over 100 bughunters have participated in the program and were rewarded over $110,000.

Sharing Knowledge

We’re pleased to announce that in 2022, we’ve made the learning opportunities for bug hunters available at our Bug Hunter University (BHU) more diverse and accessible. In addition to our existing collections of articles, which support improving your reports and avoiding invalid reports, we’ve made more than 20 instructional videos available. Clocking in at around 10 minutes each, these videos cover the most relevant learning topics and trends we’ve observed over the past years.

To make this happen, we teamed up with some of your favorite and best-known security researchers from around the globe, including LiveOverflow, PwnFunction, stacksmashing, InsiderPhD, PinkDraconian, and many more!

If you’re tired of reading our articles, or simply curious and looking for an alternative way to expand your bug hunting skills, these videos are for you. Check out our overview, or hop right in to the BHU YouTube playlist. Happy watching & learning!


Google Play

2022 was a year of change for the Google Play Security Reward Program. In May we onboarded both new teammates and some old friends to triage and lead GPSRP. We also sponsored NahamCon ‘22, BountyCon in Singapore, and NahamCon Europe’s online event. In 2023 we hope to continue to grow the program with new bug hunters and partner on more events focused on Android & Google Play apps.

Research Grants

In 2022 we continued our Vulnerability Research Grant program with success. We’ve awarded more than $250,000 in grants to over 170 security researchers. Last year we also piloted collaboration double VRP rewards for selected grants and are looking forward to expanding it even more in 2023.

If you are a Google VRP researcher and want to be considered for a Vulnerability Research Grant, make sure you opted in on your bughunters profile.

Looking Forward

Without our incredible security researchers we wouldn’t be here sharing this amazing news today. Thank you again for your continued hard work!

Also, in case you haven’t seen Hacking Google yet, make sure to check out the “Bug Hunters” episode, featuring some of our very own super talented bug hunters.

Thank you again for helping to make Google, the Internet, and our users more safe and secure! Follow us on @GoogleVRP for other news and updates.

Thank you to Adam Bacchus, Dirk Göhmann, Eduardo Vela, Sarah Jacobus, Amy Ressler, Martin Straka, Jan Keller, Tony Mendez, Rishika Hooda

Hardening Firmware Across the Android Ecosystem

Posted by Roger Piqueras Jover, Ivan Lozano, Sudhi Herle, and Stephan Somogyi, Android Team

A modern Android powered smartphone is a complex hardware device: Android OS runs on a multi-core CPU - also called an Application Processor (AP). And the AP is one of many such processors of a System On Chip (SoC). Other processors on the SoC perform various specialized tasks — such as security functions, image & video processing, and most importantly cellular communications. The processor performing cellular communications is often referred to as the baseband. For the purposes of this blog, we refer to the software that runs on all these other processors as “Firmware”.

Securing the Android Platform requires going beyond the confines of the Application Processor (AP). Android’s defense-in-depth strategy also applies to the firmware running on bare-metal environments in these microcontrollers, as they are a critical part of the attack surface of a device.

A popular attack vector within the security research community

As the security of the Android Platform has been steadily improved, some security researchers have shifted their focus towards other parts of the software stack, including firmware. Over the last decade there have been numerous publications, talks, Pwn2Own contest winners, and CVEs targeting exploitation of vulnerabilities in firmware running in these secondary processors. Bugs remotely exploitable over the air (eg. WiFi and cellular baseband bugs) are of particular concern and, therefore, are popular within the security research community. These types of bugs even have their own categorization in well known 3rd party exploit marketplaces.

Regardless of whether it is remote code execution within the WiFi SoC or within the cellular baseband, a common and resonating theme has been the consistent lack of exploit mitigations in firmware. Conveniently, Android has significant experience in enabling exploit mitigations across critical attack surfaces.

Applying years worth of lessons learned in systems hardening

Over the last few years, we have successfully enabled compiler-based mitigations in Android — on the AP — which add additional layers of defense across the platform, making it harder to build reproducible exploits and to prevent certain types of bugs from becoming vulnerabilities. Building on top of these successes and lessons learned, we’re applying the same principles to hardening the security of firmware that runs outside of Android per se, directly on the bare-metal hardware.

In particular, we are working with our ecosystem partners in several areas aimed at hardening the security of firmware that interacts with Android:

Bare-metal support

Compiler-based sanitizers have no runtime requirements in trapping mode, which provides a meaningful layer of protection we want: it causes the program to abort execution when detecting undefined behavior. As a result, memory corruption vulnerabilities that would otherwise be exploitable are now stopped entirely. To aid developers in testing, troubleshooting, and generating bug reports on debug builds, both minimal and full diagnostics modes can be enabled, which require defining and linking the requisite runtime handlers.

Most Control Flow Integrity (CFI) schemes also work for bare-metal targets in trapping mode. LLVM’s1 CFI across shared libraries scheme (cross-DSO) is the exception as it requires a runtime to be defined for the target. Shadow Call Stack, an AArch64-only feature, has a runtime component which initializes the shadow stack. LLVM does not provide this runtime for any target, so bare-metal users would need to define that runtime to use it.

The challenge

Enabling exploit mitigations in firmware running on bare metal targets is no easy feat. While the AP (Application Processor) hosts a powerful operating system (Linux) with comparatively abundant CPU and memory resources, bare metal targets are often severely resource-constrained, and are tuned to run a very specific set of functions. Any perturbation in compute and/or memory consumption introduced by enabling, for example, compiler-based sanitizers, could have a significant impact in functionality, performance, and stability.

Therefore, it is critical to optimize how and where exploit mitigations are turned on. The goal is to maximize impact — harden the most exposed attack surface — while minimizing any performance/stability impact. For example, in the case of the cellular baseband, we recommend focusing on code and libraries responsible for parsing messages delivered over the air (particularly for pre-authentication protocols such as RRC and NAS, which are the most exposed attack surface), libraries encoding/decoding complex formats (for example ASN.1), and libraries implementing IMS (IP Multimedia System) functionality, or parsing SMS and/or MMS.

Fuzzing and Vulnerability Rewards Program

Enabling exploit mitigations and compiler-based sanitizers are excellent techniques to minimize the chances of unknown bugs becoming exploitable. However, it is also important to continuously look for, find, and patch bugs.

Fuzzing continues to be a highly efficient method to find impactful bugs. It’s also been proven to be effective for signaling larger design issues in code. Our team partners closely with Android teams working on fuzzing and security assessments to leverage their expertise and tools with bare metal targets.

This collaboration also allowed us to scale fuzzing activities across Google by deploying central infrastructure that allows fuzzers to run in perpetuity. This is a high-value approach known as continuous fuzzing.

In parallel, we also accept and reward external contributions via our Vulnerability Rewards Program. Along with the launch of Android 13, we updated the severity guidelines to further highlight remotely exploitable bugs in connectivity firmware. We look forward to the contributions from the security research community to help us find and patch bugs in bare metal targets.

On the horizon

In Android 12 we announced support for Rust in the Android platform, and Android 13 is the first release with a majority of new code written in a memory safe language. We see a lot of potential in also leveraging memory-safe languages for bare metal targets, particularly for high risk and exposed attack surface.

Hardening firmware running on bare metal to materially increase the level of protection - across more surfaces in Android - is one of the priorities of Android Security. Moving forward, our goal is to expand the use of these mitigation technologies for more bare metal targets, and we strongly encourage our partners to do the same. We stand ready to assist our ecosystem partners to harden bare metal firmware.

Special thanks to our colleagues who contributed to this blog post and our firmware security hardening efforts: Diana Baker, Farzan Karimi, Jeffrey Vander Stoep, Kevin Deus, Eugene Rodionov, Pirama Arumuga Nainar, Sami Tolvanen, Stephen Hines, Xuan Xing, Yomna Nasser.

Notes

  1. LLVM - is a compiler framework used by multiple programming languages ↩

Expanding the App Defense Alliance

Posted by Brooke Davis, Android Security and Privacy Team

The App Defense Alliance launched in 2019 with a mission to protect Android users from bad apps through shared intelligence and coordinated detection between alliance partners. Earlier this year, the App Defense Alliance expanded to include new initiatives outside of malware detection and is now the home for several industry-led collaborations including Malware Mitigation, MASA (Mobile App Security Assessment) & CASA (Cloud App Security Assessment). With a new dedicated landing page at appdefensealliance.dev, the ADA has an expanded mission to protect Android users by removing threats while improving app quality across the ecosystem. Let’s walk through some of the latest program updates from the past year, including the addition of new ADA members.

Malware Mitigation

Together, with the founding ADA members - Google, ESET, Lookout, and Zimperium, the alliance has been able to reduce the risk of app-based malware and better protect Android users. These partners have access to mobile apps as they are being submitted to the Google Play Store and scan thousands of apps daily, acting as another, vital set of eyes prior to an app going live on Play. Knowledge sharing and industry collaboration are important aspects in securing the world from attacks and that’s why we’re continuing to invest in the program.


New ADA Members

We’re excited to see the ADA expand with the additions of McAfee and Trend Micro. Both McAfee and Trend Micro are leaders in the antivirus space and we look forward to their contributions to the program.

Mobile App Security Assessment (MASA)

With consumers spending four to five hours per day in mobile apps, ensuring the safety of these services is more important than ever. According to Data.ai, the pandemic accelerated existing mobile habits - with app categories like finance growing 25% YoY and users spending over 100 billion hours in shopping apps.

That’s why the ADA introduced MASA (Mobile App Security Assessment), which allows developers to have their apps independently validated against the Mobile Application Security Verification Standard (MASVS standard) under the OWASP Mobile Application Security project. The project’s mission is to “Define the industry standard for mobile application security,” and has been used by both public and private sector organizations as a form of industry best practices when it comes to mobile application security. Developers can work directly with an ADA Authorized Lab to have their apps evaluated against a set of MASVS L1 requirements. Once successful, the app’s validation is listed in the recently launched App Validation Directory, which provides users a single place to view all app validations. The Directory also allows users to access more assessment details including validation date, test lab, and a report showing all test steps and requirements. The Directory will be updated over time with new features and search functionality to make it more user friendly.

The Google Play Store is the first commercial app store to recognize and display a badge for any app that has completed an independent security review through ADA MASA. The badge is displayed within an app’s respective Data Safety section.

This MASA program launched in beta earlier this year and is now available for all developers. We’ve seen strong early developer interest with leading apps across a diverse set of categories completing validation including Roblox, Uber, PayPal, Threema, Google Photos, YouTube and many more. On average, developers have completed validation within a month and resolved two outstanding issues identified by a security lab.

To learn more about the program and to help developers get started, there’s a Play Academy course dedicated to independent security review. Check out the interactive guidance on the Academy for App Success and get started today!

Cloud App Security Assessment (CASA)

As the industry continues to evolve and software connects more systems through complex cloud-to-cloud integrations, focusing on the security of cloud applications and their supporting infrastructure becomes increasingly critical. CASA (Cloud App Security Assessment) leverages the work set forth in OWASP’s Application Security Verification Standard ASVS to provide a consistent set of requirements to harden security for any application. The CASA framework provides multiple assurance levels in which low-risk cloud applications can be evaluated using either a self assessment or automated scan. For applications which present higher risk (such as a large user base, recent security breach, or processes highly sensitive data), an Authorized Lab may perform an assessment.

Further, the CASA accelerator provides developers with a workflow that minimizes the required checks depending on the developer's current valid certifications. The CASA checks have been mapped to 10 certifications and frameworks which eliminate redundant testing while lowering the cost of the assessment. Google is continuing to invest in this space with plans to use ASVS more proactively with the developer community next year.

It's been amazing to see the ADA grow this year and we are excited for the continued progress and expansion around the alliance’s mission.

Trust in transparency: Private Compute Core

Posted by Dave Kleidermacher, Dianne Hackborn, and Eugenio Marchiori

We care deeply about privacy. We also know that trust is built by transparency. This blog, and the technical paper reference within, is an example of that commitment: we describe an important new Android privacy infrastructure called Private Compute Core (PCC).

Some of our most exciting machine learning features use continuous sensing data — information from the microphone, camera, and screen. These features keep you safe, help you communicate, and facilitate stronger connections with people you care about. To unlock this new generation of innovative concepts, we built a specialized sandbox to privately process and protect this data.

Android Private Compute Core

PCC is a secure, isolated data processing environment inside of the Android operating system that gives you control of the data inside, such as deciding if, how, and when it is shared with others. This way, PCC can enable features like Live Translate without sharing continuous sensing data with service providers, including Google.

PCC is part of Protected Computing, a toolkit of technologies that transform how, when, and where data is processed to technically ensure its privacy and safety. For example, by employing cloud enclaves, edge processing, or end-to-end encryption we ensure sensitive data remains in exclusive control of the user.

How Private Compute Core works

PCC is designed to enable innovative features while keeping the data needed for them confidential from other subsystems. We do this by using techniques such as limiting Interprocess Communications (IPC) binds and using isolated processes. These are included as part of the Android Open Source Project and controlled by publicly available surfaces, such as Android framework APIs. For features that run inside PCC, continuous sensing data is processed safely and seamlessly while keeping it confidential.

To stay useful, any machine learning feature has to get better over time. To keep the models that power PCC features up to date, while still keeping the data private, we leverage federated learning and analytics. Network calls to improve the performance of these models can be monitored using Private Compute Services.

Let us show you our work

The publicly-verifiable architectures in PCC demonstrate how we strive to deliver confidentiality and control, and do it in a way that is verifiable and visible to users. In addition to this blog, we provide this transparency through public documentation and open-source code — we hope you'll have a look below.

To explain in even more detail, we’ve published a technical whitepaper for researchers and interested members of the community. In it, we describe data protections in-depth, the processes and mechanisms we’ve built, and include diagrams of the privacy structures for continuous sensing features.

Private Compute Services was recently open-sourced as well, and we invite our Android community to inspect the code that controls the data management and egress policies. We hope you'll examine and report back on PCC's implementation, so that our own documentation is not the only source of analysis.

Our commitment to transparency

Being transparent and engaged with users, developers, researchers, and technologists around the world is part of what makes Android special and, we think, more trustworthy. The paradigm of distributed trust, where credibility is built up from verification by multiple trusted sources, continues to extend this core value. Open sourcing the mechanisms for data protection and processes is one step towards making privacy verifiable. The next step is verification by the community — and we hope you'll join in.

We'll continue sharing our progress and look forward to hearing feedback from our users and community on the evolution of Private Compute Core and data privacy at Google.

Memory Safe Languages in Android 13

Posted by Jeffrey Vander Stoep

For more than a decade, memory safety vulnerabilities have consistently represented more than 65% of vulnerabilities across products, and across the industry. On Android, we’re now seeing something different - a significant drop in memory safety vulnerabilities and an associated drop in the severity of our vulnerabilities.

Looking at vulnerabilities reported in the Android security bulletin, which includes critical/high severity vulnerabilities reported through our vulnerability rewards program (VRP) and vulnerabilities reported internally, we see that the number of memory safety vulnerabilities have dropped considerably over the past few years/releases. From 2019 to 2022 the annual number of memory safety vulnerabilities dropped from 223 down to 85.

This drop coincides with a shift in programming language usage away from memory unsafe languages. Android 13 is the first Android release where a majority of new code added to the release is in a memory safe language.

As the amount of new memory-unsafe code entering Android has decreased, so too has the number of memory safety vulnerabilities. From 2019 to 2022 it has dropped from 76% down to 35% of Android’s total vulnerabilities. 2022 is the first year where memory safety vulnerabilities do not represent a majority of Android’s vulnerabilities.

While correlation doesn’t necessarily mean causation, it’s interesting to note that the percent of vulnerabilities caused by memory safety issues seems to correlate rather closely with the development language that’s used for new code. This matches the expectations published in our blog post 2 years ago about the age of memory safety vulnerabilities and why our focus should be on new code, not rewriting existing components. Of course there may be other contributing factors or alternative explanations. However, the shift is a major departure from industry-wide trends that have persisted for more than a decade (and likely longer) despite substantial investments in improvements to memory unsafe languages.

We continue to invest in tools to improve the safety of our C/C++. Over the past few releases we’ve introduced the Scudo hardened allocator, HWASAN, GWP-ASAN, and KFENCE on production Android devices. We’ve also increased our fuzzing coverage on our existing code base. Vulnerabilities found using these tools contributed both to prevention of vulnerabilities in new code as well as vulnerabilities found in old code that are included in the above evaluation. These are important tools, and critically important for our C/C++ code. However, these alone do not account for the large shift in vulnerabilities that we’re seeing, and other projects that have deployed these technologies have not seen a major shift in their vulnerability composition. We believe Android’s ongoing shift from memory-unsafe to memory-safe languages is a major factor.

Rust for Native Code

In Android 12 we announced support for the Rust programming language in the Android platform as a memory-safe alternative to C/C++. Since then we’ve been scaling up our Rust experience and usage within the Android Open Source Project (AOSP).

As we noted in the original announcement, our goal is not to convert existing C/C++ to Rust, but rather to shift development of new code to memory safe languages over time.

In Android 13, about 21% of all new native code (C/C++/Rust) is in Rust. There are approximately 1.5 million total lines of Rust code in AOSP across new functionality and components such as Keystore2, the new Ultra-wideband (UWB) stack, DNS-over-HTTP3, Android’s Virtualization framework (AVF), and various other components and their open source dependencies. These are low-level components that require a systems language which otherwise would have been implemented in C++.

Security impact

To date, there have been zero memory safety vulnerabilities discovered in Android’s Rust code.


We don’t expect that number to stay zero forever, but given the volume of new Rust code across two Android releases, and the security-sensitive components where it’s being used, it’s a significant result. It demonstrates that Rust is fulfilling its intended purpose of preventing Android’s most common source of vulnerabilities. Historical vulnerability density is greater than 1/kLOC (1 vulnerability per thousand lines of code) in many of Android’s C/C++ components (e.g. media, Bluetooth, NFC, etc). Based on this historical vulnerability density, it’s likely that using Rust has already prevented hundreds of vulnerabilities from reaching production.

What about unsafe Rust?

Operating system development requires accessing resources that the compiler cannot reason about. For memory-safe languages this means that an escape hatch is required to do systems programming. For Java, Android uses JNI to access low-level resources. When using JNI, care must be taken to avoid introducing unsafe behavior. Fortunately, it has proven significantly simpler to review small snippets of C/C++ for safety than entire programs. There are no pure Java processes in Android. It’s all built on top of JNI. Despite that, memory safety vulnerabilities are exceptionally rare in our Java code.

Rust likewise has the unsafe{} escape hatch which allows interacting with system resources and non-Rust code. Much like with Java + JNI, using this escape hatch comes with additional scrutiny. But like Java, our Rust code is proving to be significantly safer than pure C/C++ implementations. Let’s look at the new UWB stack as an example.

There are exactly two uses of unsafe in the UWB code: one to materialize a reference to a Rust object stored inside a Java object, and another for the teardown of the same. Unsafe was actively helpful in this situation because the extra attention on this code allowed us to discover a possible race condition and guard against it.

In general, use of unsafe in Android’s Rust appears to be working as intended. It’s used rarely, and when it is used, it’s encapsulating behavior that’s easier to reason about and review for safety.

Safety measures make memory-unsafe languages slow

Mobile devices have limited resources and we’re always trying to make better use of them to provide users with a better experience (for example, by optimizing performance, improving battery life, and reducing lag). Using memory unsafe code often means that we have to make tradeoffs between security and performance, such as adding additional sandboxing, sanitizers, runtime mitigations, and hardware protections. Unfortunately, these all negatively impact code size, memory, and performance.

Using Rust in Android allows us to optimize both security and system health with fewer compromises. For example, with the new UWB stack we were able to save several megabytes of memory and avoid some IPC latency by running it within an existing process. The new DNS-over-HTTP/3 implementation uses fewer threads to perform the same amount of work by using Rust’s async/await feature to process many tasks on a single thread in a safe manner.

What about non-memory-safety vulnerabilities?

The number of vulnerabilities reported in the bulletin has stayed somewhat steady over the past 4 years at around 20 per month, even as the number of memory safety vulnerabilities has gone down significantly. So, what gives? A few thoughts on that.

A drop in severity

Memory safety vulnerabilities disproportionately represent our most severe vulnerabilities. In 2022, despite only representing 36% of vulnerabilities in the security bulletin, memory-safety vulnerabilities accounted for 86% of our critical severity security vulnerabilities, our highest rating, and 89% of our remotely exploitable vulnerabilities. Over the past few years, memory safety vulnerabilities have accounted for 78% of confirmed exploited “in-the-wild” vulnerabilities on Android devices.

Many vulnerabilities have a well defined scope of impact. For example, a permissions bypass vulnerability generally grants access to a specific set of information or resources and is generally only reachable if code is already running on the device. Memory safety vulnerabilities tend to be much more versatile. Getting code execution in a process grants access not just to a specific resource, but everything that that process has access to, including attack surface to other processes. Memory safety vulnerabilities are often flexible enough to allow chaining multiple vulnerabilities together. The high versatility is perhaps one reason why the vast majority of exploit chains that we have seen use one or more memory safety vulnerabilities.

With the drop in memory safety vulnerabilities, we’re seeing a corresponding drop in vulnerability severity.



With the decrease in our most severe vulnerabilities, we’re seeing increased reports of less severe vulnerability types. For example, about 15% of vulnerabilities in 2022 are DoS vulnerabilities (requiring a factory reset of the device). This represents a drop in security risk.

Android appreciates our security research community and all contributions made to the Android VRP. We apply higher payouts for more severe vulnerabilities to ensure that incentives are aligned with vulnerability risk. As we make it harder to find and exploit memory safety vulnerabilities, security researchers are pivoting their focus towards other vulnerability types. Perhaps the total number of vulnerabilities found is primarily constrained by the total researcher time devoted to finding them. Or perhaps there’s another explanation that we have not considered. In any case, we hope that if our vulnerability researcher community is finding fewer of these powerful and versatile vulnerabilities, the same applies to adversaries.

Attack surface

Despite most of the existing code in Android being in C/C++, most of Android’s API surface is implemented in Java. This means that Java is disproportionately represented in the OS’s attack surface that is reachable by apps. This provides an important security property: most of the attack surface that’s reachable by apps isn’t susceptible to memory corruption bugs. It also means that we would expect Java to be over-represented when looking at non-memory safety vulnerabilities. It’s important to note however that types of vulnerabilities that we’re seeing in Java are largely logic bugs, and as mentioned above, generally lower in severity. Going forward, we will be exploring how Rust’s richer type system can help prevent common types of logic bugs as well.

Google’s ability to react

With the vulnerability types we’re seeing now, Google’s ability to detect and prevent misuse is considerably better. Apps are scanned to help detect misuse of APIs before being published on the Play store and Google Play Protect warns users if they have abusive apps installed.

What’s next?

Migrating away from C/C++ is challenging, but we’re making progress. Rust use is growing in the Android platform, but that’s not the end of the story. To meet the goals of improving security, stability, and quality Android-wide, we need to be able to use Rust anywhere in the codebase that native code is required. We’re implementing userspace HALs in Rust. We’re adding support for Rust in Trusted Applications. We’ve migrated VM firmware in the Android Virtualization Framework to Rust. With support for Rust landing in Linux 6.1 we’re excited to bring memory-safety to the kernel, starting with kernel drivers.

As Android migrates away from C/C++ to Java/Kotlin/Rust, we expect the number of memory safety vulnerabilities to continue to fall. Here’s to a future where memory corruption bugs on Android are rare!

Google Pixel 7 and Pixel 7 Pro: The next evolution in mobile security

Dave Kleidermacher, Jesse Seed, Brandon Barbello, Sherif Hanna, Eugene Liderman, Android, Pixel, and Silicon Security Teams

Every day, billions of people around the world trust Google products to enrich their lives and provide helpful features – across mobile devices, smart home devices, health and fitness devices, and more. We keep more people safe online than anyone else in the world, with products that are secure by default, private by design and that put you in control. As our advancements in knowledge and computing grow to deliver more help across contexts, locations and languages, our unwavering commitment to protecting your information remains.

That’s why Pixel phones are designed from the ground up to help protect you and your sensitive data while keeping you in control. We’re taking our industry-leading approach to security and privacy to the next level with Google Pixel 7 and Pixel 7 Pro, our most secure and private phones yet, which were recently recognized as the highest rated for security when tested among other smartphones by a third-party global research firm.1

Pixel phones also get better every few months with Feature Drops that provide the latest product updates, tips and tricks from Google. And Pixel 7 and Pixel 7 Pro users will receive at least five years of security updates2, so your Pixel gets even more secure over time.

Your protection, built into Pixel

Your digital life and most sensitive information lives on your phone: financial information, passwords, personal data, photos – you name it. With Google Tensor G2 and our custom Titan M2 security chip, Pixel 7 and Pixel 7 Pro have multiple layers of hardware security to help keep you and your personal information safe. We take a comprehensive, end-to-end approach to security with verifiable protections at each layer - the network, application, operating system and multiple layers on the silicon itself. If you use Pixel for your business, this approach helps protect your company data, too.

Google Tensor G2 is Pixel’s newest powerful processor custom built with Google AI, and makes Pixel 7 faster, more efficient and secure3. Every aspect of Tensor G2 was designed to improve Pixel's performance and efficiency for great battery life, amazing photos and videos.

Tensor’s built-in security core works with our Titan M2 security chip to keep your personal information, PINs and passwords safe. Titan family chips are also used to protect Google Cloud data centers and Chromebooks, so the same hardware that protects Google servers also secures your sensitive information stored on Pixel.

And, in a first for Google, Titan M2 hardware has now been certified under Common Criteria PP0084: the international gold standard for hardware security components also used for identity, SIM cards, and bankcard security chips.4 This means that the Titan M2 hardware meets the same rigorous protection guidelines trusted by banks, carriers, and governments.

To achieve the certification we went through rigorous third party lab testing by SGS Brightsight, a leading international security lab, and received certification against CC PP0084 with AVA_VAN.5 for the Titan M2 hardware and cryptography library from the Netherlands scheme for Certification in the Area of IT Security (NSCIB). Of all those numbers and acronyms the part we’re most proud of is that Titan hardware passed the highest level of vulnerability assessment (AVA_VAN.5) - the truest measure of resilience to advanced, methodical attacks.

This process took us more than three years to complete. The certification not only requires chip hardware to resist invasive penetration testing, but also mandates audits of the chip design and manufacturing process itself. The benefit for consumers? The now certified Titan M2 chip makes your phone even more resilient to sophisticated attacks.5

Private by design

Evolving our security and privacy standards to our fast-paced world requires new approaches as well. Earlier this year at I/O, we introduced Protected Computing, a toolkit of technologies that transforms how, when, and where personal data is processed to protect your privacy and security. Our approach focuses on:

  1. Minimizing your data footprint, by shrinking the amount of personally identifiable data altogether
  2. De-identifying data, with a range of anonymization techniques so it’s not linked to you
  3. Restricting data access using technologies like end-to-end encryption and secure enclaves.

Many elements of Protected Computing can be found on the new Pixel 7:

On Android, Private Compute Core keeps your information and AI-driven personalizations private with on-device processing. Data from features like Now Playing, Live Caption and Smart Reply in Messages are all processed on device and are never sent to Google to maintain your privacy. And even your device backups to the cloud are end-to-end encrypted using Titan in the cloud.6

With Google Tensor G2, Pixel’s advanced privacy protection also now covers audio data from events like cough and snore detection on Pixel 7.7 Audio data from cough and snore detection is never stored by or sent to Google to maintain your privacy.

On Pixel 7, Tensor G2 helps safeguard your system with the Android Virtualization Framework, unlocking improved security protections like enabling system update integrity checking to occur on-the-fly, reducing boot time after an update.

Extra protection when you’re online

Helping to keep you safe when you use your phone to browse the web and use apps is also critical. This is where a Virtual Private Network (VPN) comes in. A VPN helps protect your online activity from anyone who might try to access it by encrypting your network traffic to turn it into an unreadable format, and masking your original IP address. Typically, if you want a VPN on your phone, you need to get one from a third party.

To ensure more people have access to enhanced security, later this year, Pixel 7 and Pixel 7 Pro owners will be able to use VPN by Google One, at no extra cost.8 VPN by Google One is verifiably private, and will allow you to tap into Google’s world-class security for peace of mind when you connect online. With VPN by Google One, Pixel helps protect your online activity at a network level. Think of it like an extra layer of protection for your online security.

VPN by Google One creates a high-performance secure connection to the web so your browsing and app data is sent and received via an encrypted pathway. A few simple taps will activate the VPN to help keep your network traffic private from internet providers and hackers, giving you peace of mind when using cellular data, home Wi-Fi, and especially when connected to public networks, like a café or airport Wi-Fi. No need to worry about online intruders, hackers, or unsecure networks.

Unlike traditional VPN services, VPN by Google One uses Protected Computing to technically make it impossible for anyone at a network level, even VPN by Google One, to link your online traffic with your account or identity. VPN by Google One will be available at no extra cost as long as your phone continues to receive security updates. See here to learn more about VPN by Google One.

More protection and privacy with Android 13

Pixel 7 and Pixel 7 Pro have built-in anti-phishing protections from Android that scan for potential threats from phone calls, text messages and emails, and more anti-phishing protections enabled out-of-the-box than smartphones from leading competitors.9 In fact, Messages alone protects consumers against 1.5 billion spam messages per month.

Android also resets permissions for apps you haven’t used for an extended time. In a typical month, Android automatically resets more than 3 billion permissions affecting more than 1 billion installed apps. Similarly, if you use clipboard on Android 13, your history is automatically deleted after a period of time. This blocks apps running in the foreground from seeing old information that you previously copied.

You’re in control


Core to your safety is knowing that you’re in control. You always have control over your settings and devices across all of our products. With Android 13, coming soon through a Feature Drop, Pixel 7 and Pixel 7 Pro will give you additional ways to stay in control of your privacy and what you share with first and third-party apps. With Quick Settings, you can act on security issues as they arise, or review which apps are running in the background and easily stop them. You’ll have a single destination for reviewing your security and privacy settings, risk levels and information, making it easier to manage your safety status.

With this new experience, you can review actionable steps to improve your safety status, like revoking a permission or app. This page will also have new action cards to notify you of any safety risks and provide timely recommendations on how to enhance your privacy. And with a single tap, you can grant or remove permissions to data that you don’t want to share with compatible apps. This will be coming soon first to Pixel devices later this year, and other Android phones soon after.

Verifiably secure

As computing extends to more devices and use cases, Google is committed to innovating in security and being transparent about the processes that we take to get there. We are leading the industry in verifiable security by not only having products that are tested against real-world threats (like advanced spam, phishing and malware attacks), but also in publishing the results of penetration tests, security audits, and industry certifications across our Pixel and Nest products.

Another way to verify our security is through our Android and Google Devices Security Reward Program where we reward security researchers who find vulnerabilities across products, including Pixel, Nest and Fitbit. Last year on Android, we awarded nearly $3 million dollars, creating a valuable feedback loop between us and the security research community and, most importantly, helping us keep our users safe.

To learn more about Pixel 7 and Pixel 7 Pro, check out the Google Store.

Notes

  1. Based on third-party global research firm. Evaluation considered features that may not be available in all countries. See here for more information.  ↩

  2. Android version updates and feature drops for at least 3 years from when the device first became available on the Google Store in the US. Android security updates for at least 5 years from when the device first became available on the Google Store in the US. See g.co/pixel/updates for details. ↩

  3. Compared to Pixel 6. Speed and efficiency claims based on internal testing on pre-production devices.  ↩

  4. Common Criteria certification for hardware and cryptographic library (CC PP0084 EAL4+, AVA_VAN.5 and ALC_DVS.2). See g.co/pixel/certifications for details. ↩

  5. Compared to Pixel 5a and earlier Pixel phones.  ↩

  6. Excludes MMS attachments and Google Photos. ↩

  7. Not intended to diagnose, cure, mitigate, prevent or treat any disease or condition. Consult your healthcare professional if you have questions about your health. See g.co/pixel/digitalwellbeing for more information.  ↩

  8. Coming soon. Restrictions apply. Some data is not transmitted through VPN. Not available in all countries. All other Google One membership benefits sold separately. This VPN offer does not impact price or benefits of Google One Premium plan. Use of VPN may increase data costs depending on your plan. See g.co/pixel/vpn for details. ↩

  9. Based on third-party research funded by Google LLC in June 2022. Evaluation based on no-cost smartphone features enabled by default. Some features may not be available in all countries. See here for more information. ↩

DNS-over-HTTP/3 in Android

Posted by Matthew Maurer and Mike Yu, Android team

To help keep Android users’ DNS queries private, Android supports encrypted DNS. In addition to existing support for DNS-over-TLS, Android now supports DNS-over-HTTP/3 which has a number of improvements over DNS-over-TLS.

Most network connections begin with a DNS lookup. While transport security may be applied to the connection itself, that DNS lookup has traditionally not been private by default: the base DNS protocol is raw UDP with no encryption. While the internet has migrated to TLS over time, DNS has a bootstrapping problem. Certificate verification relies on the domain of the other party, which requires either DNS itself, or moves the problem to DHCP (which may be maliciously controlled). This issue is mitigated by central resolvers like Google, Cloudflare, OpenDNS and Quad9, which allow devices to configure a single DNS resolver locally for every network, overriding what is offered through DHCP.

In Android 9.0, we announced the Private DNS feature, which uses DNS-over-TLS (DoT) to protect DNS queries when enabled and supported by the server. Unfortunately, DoT incurs overhead for every DNS request. An alternative encrypted DNS protocol, DNS-over-HTTPS (DoH), is rapidly gaining traction within the industry as DoH has already been deployed by most public DNS operators, including the Cloudflare Resolver and Google Public DNS. While using HTTPS alone will not reduce the overhead significantly, HTTP/3 uses QUIC, a transport that efficiently multiplexes multiple streams over UDP using a single TLS session with session resumption. All of these features are crucial to efficient operation on mobile devices.

DNS-over-HTTP/3 (DoH3) support was released as part of a Google Play system update, so by the time you’re reading this, Android devices from Android 11 onwards1 will use DoH3 instead of DoT for well-known2 DNS servers which support it. Which DNS service you are using is unaffected by this change; only the transport will be upgraded. In the future, we aim to support DDR which will allow us to dynamically select the correct configuration for any server. This feature should decrease the performance impact of encrypted DNS.

Performance

DNS-over-HTTP/3 avoids several problems that can occur with DNS-over-TLS operation:

  • As DoT operates on a single stream of requests and responses, many server implementations suffer from head-of-line blocking3. This means that if the request at the front of the line takes a while to resolve (possibly because a recursive resolution is necessary), responses for subsequent requests that would have otherwise been resolved quickly are blocked waiting on that first request. DoH3 by comparison runs each request over a separate logical stream, which means implementations will resolve requests out-of-order by default.
  • Mobile devices change networks frequently as the user moves around. With DoT, these events require a full renegotiation of the connection. By contrast, the QUIC transport HTTP/3 is based on can resume a suspended connection in a single RTT.
  • DoT intends for many queries to use the same connection to amortize the cost of TCP and TLS handshakes at the start. Unfortunately, in practice several factors (such as network disconnects or server TCP connection management) make these connections less long-lived than we might like. Once a connection is closed, establishing the connection again requires at least 1 RTT.

    In unreliable networks, DoH3 may even outperform traditional DNS. While unintuitive, this is because the flow control mechanisms in QUIC can alert either party that packets weren’t received. In traditional DNS, the timeout for a query needs to be based on expected time for the entire query, not just for the resolver to receive the packet.

Field measurements during the initial limited rollout of this feature show that DoH3 significantly improves on DoT’s performance. For successful queries, our studies showed that replacing DoT with DoH3 reduces median query time by 24%, and 95th percentile query time by 44%. While it might seem suspect that the reported data is conditioned on successful queries, both DoT and DoH3 resolve 97% of queries successfully, so their metrics are directly comparable. UDP resolves only 83% of queries successfully. As a result, UDP latency is not directly comparable to TLS/HTTP3 latency because non-connection-oriented protocols have a different notion of what a "query" is. We have still included it for rough comparison.

Memory Safety

The DNS resolver processes input that could potentially be controlled by an attacker, both from the network and from apps on the device. To reduce the risk of security vulnerabilities, we chose to use a memory safe language for the implementation.

Fortunately, we’ve been adding Rust support to the Android platform. This effort is intended exactly for cases like this — system level features which need to be performant or low level (both in this case) and which would carry risk to implement in C++. While we’ve previously launched Keystore 2.0, this represents our first foray into Rust in Mainline Modules. Cloudflare maintains an HTTP/3 library called quiche, which fits our use case well, as it has a memory-safe implementation, few dependencies, and a small code size. Quiche also supports use directly from C++. We considered this, but even the request dispatching service had sufficient complexity that we chose to implement that portion in Rust as well.

We built the query engine using the Tokio async framework to simultaneously handle new requests, incoming packet events, control signals, and timers. In C++, this would likely have required multiple threads or a carefully crafted event loop. By leveraging asynchronous in Rust, this occurs on a single thread with minimal locking4. The DoH3 implementation is 1,640 lines and uses a single runtime thread. By comparison, DoT takes 1,680 lines while managing less and using up to 4 threads per DoT server in use.

Safety and Performance — Together at Last

With the introduction of Rust, we are able to improve both security and the performance at the same time. Likewise, QUIC allows us to improve network performance and privacy simultaneously. Finally, Mainline ensures that such improvements are able to make their way to more Android users sooner.

Acknowledgements

Special thanks to Luke Huang who greatly contributed to the development of this feature, and Lorenzo Colitti for his in-depth review of the technical aspects of this post.

  1. Some Android 10 devices which adopted Google Play system updates early will also receive this feature. ↩

  2. Google DNS and Cloudflare DNS at launch, others may be added in the future. ↩

  3. DoT can be implemented in a way that avoids this problem, as the client must accept server responses out of order. However, in practice most servers do not implement this reordering. ↩

  4. There is a lock used for the SSL context which is accessed once per DNS server, and another on the FFI when issuing a request. The FFI lock could be removed with changes to the C++ side, but has remained because it is low contention. ↩