June 3, 2023

Google revealed that attackers are increasingly leveraging a specific class of vulnerabilities derived from side-channels built into the web platform, to extract sensitive data out of any web application. Dubbed cross-site leaks (XS-Leaks),

Side-channel attacks

Attackers use the existing side-channels on the web to leak sensitive information about the users from other web applications, such as details about their local environment or their internal networks.

  • A team of security researchers had discovered new side-channel attacks that could allow attackers to access the sensitive data on Intel CPUs.
  • Researchers from the University of California and Tsinghua University also reported a series of critical vulnerabilities dubbed SAD DNS attacks that could lead to a revival of DNS cache poisoning attacks.

Google’s XS support

To encourage research into the issue of cross-site leaks of user information, Google has recently set up a new site for XS-Leaks.It is basically a collection of browser-based side-channel attack vectors. 

  • These attack vectors highlight a set of challenges for web browser developers and security engineers, enabling the development of a comprehensive defense mechanism.
  • The XS-Leaks wiki site basically includes information about the principles behind cross-site leaks, common attacks, and proposes defense mechanisms to stop these attacks.

The site is an open knowledge base to which the security community is invited to participate, and where experts can share information about offensive and defensive techniques.

  • XS-Leaks takes advantage of the web’s core principle of composability. It allows websites to interact with each other and abuse legitimate mechanisms to infer information about the user.
  • Each attack described on the site is accompanied by an overview of security features such as Cross-Origin Opener Policy, Cross-Origin Resource Policy, Fetch Metadata Request Headers, and SameSite cookies that can thwart or mitigate it.

Final words

Recent discoveries suggest that side-channel attacks are still in the development phase and their true potential in XS-Leak attacks is yet to be realized. It is believed that projects such as the XS-Leak wiki can help prevent or mitigate these attacks by providing appropriate frameworks and guidelines for security teams to counter such threats.

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