The web is an ecosystem built on openness and composability. It is an excellent platform for building capable applications, and it powers thousands of services created and maintained by engineers at Google that are depended on by billions of users. However, the web's open design also allows unrelated applications to sometimes interact with each other in ways which may undermine the platform's security guarantees.
Increasingly, security issues discovered in modern web applications hinge upon the misuse of long-standing web platform behaviors, allowing unsavory sites to reveal information about the user or their data in other web applications. This class of issues, broadly referred to as cross-site leaks (XS-Leaks), poses interesting challenges for security engineers and web browser developers due to a diversity of attacks and the complexity of building comprehensive defenses.
To promote a better understanding of these issues and protect the web from them, today marks the launch of the XS-Leaks wiki—an open knowledge base to which the security community is invited to participate, and where researchers can share information about new attacks and defenses.
The XS-Leaks wiki
Available at xsleaks.dev (code on GitHub), the wiki explains the principles behind cross-site leaks, discusses common attacks, and proposes defense mechanisms aimed at mitigating these attacks. The wiki is composed of smaller articles that showcase the details of each cross-site leak, their implications, proof-of-concept code to help demonstrate the issue, and effective defenses.
To improve the state of web security, we're inviting the security community to work with us on expanding the XS-Leaks wiki with information about new offensive and defensive techniques.
An important goal of the wiki is to help web developers understand the defense mechanisms offered by web browsers that can comprehensively protect their web applications from various kinds of cross-site leaks.
Each attack described in the wiki is accompanied by an overview of security features which can thwart or mitigate it; the wiki aims to provide actionable guidance to assist developers in the adoption of new browser security features such as Fetch Metadata Request Headers, Cross-Origin Opener Policy, Cross-Origin Resource Policy, and SameSite cookies.
The Security Team at Google has benefited from over a decade of productive collaboration with security experts and browser engineers to improve the security of the web platform. We hope this new resource encourages further research into creative attacks and robust defenses for a major class of web security threats. We're excited to work together with the community to continue making the web safer for all users.
Special thanks to Manuel Sousa for starting the wiki as part of his internship project at Google, and to the contributors to the xsleaks GitHub repository for their original research in this area.