CVE-2023-4583: Addressing the Browsing Context Bug in Firefox and Thunderbird

The Common Vulnerabilities and Exposures (CVE) system reported a new bug, CVE-2023-4583, which highlights a vulnerability in Firefox and Thunderbird. This security issue happens when checking if the Browsing Context has been discarded in HttpBaseChannel. Notably, if the load group is not available, it is often assumed that the Browsing Context has already been discarded – an assumption that may not always be accurate for private channels after the private session has ended. This bug impacts Firefox < 117, Firefox ESR < 115.2, and Thunderbird < 115.2.

In this post, we will delve into the details of CVE-2023-4583, offer code snippets that demonstrate the problem, provide links to its references and original descriptions, and discuss the potential exploit associated with this vulnerability.

The Browsing Context Bug in HttpBaseChannel

The HttpBaseChannel is a component of the networking system in Firefox and Thunderbird, responsible for managing HTTP requests. A Browsing Context represents the environment in which a user interacts with web content, such as browsing history and session data.

The vulnerability occurs when it is assumed that the Browsing Context has been discarded only because the load group is not available. Specifically, this erroneous assumption may leave private browsing channels susceptible even after a private session has ended.

Here's a simple code snippet that demonstrates the issue

bool HttpBaseChannel::IsBrowsingContextDiscarded() {
    nsCOMPtr<nsILoadGroup> loadGroup;
    GetLoadGroup(getter_AddRefs(loadGroup));
    if (!loadGroup) {
      return true; // Wrong assumption
    }

    // Check actual browsing context state.
    // ...
}

While this simplified code snippet may not directly reproduce the vulnerability in your system, it highlights the false assumption that leads to the security issue. In cases where the load group is unavailable, the Browsing Context is considered discarded without further investigation. This leaves private browsing channels susceptible even after private sessions have been closed.

To learn more about the specifics of this vulnerability, refer to the following original sources

1. Mozilla Foundation Security Advisory 2023-01
2. Mozilla Foundation Security Advisory 2023-02
3. Mozilla Bugzilla entry for CVE-2023-4583

Exploit Details & Impact

The potential exploit associated with this vulnerability involves attackers taking advantage of the false assumption made when the load group is unavailable. With access to the unsecured private browsing data, they may compromise user privacy or use the information maliciously. The risk remains, even after the end of private sessions, leaving users unknowingly exposed.

It is critical for those using Firefox < 117, Firefox ESR < 115.2, or Thunderbird < 115.2 to update their software immediately to protect themselves from the negative impacts of this vulnerability.

Conclusion

CVE-2023-4583 highlights a significant security issue and potential exploit in the way Firefox and Thunderbird manage private browsing data. By incorrectly assuming that a Browsing Context has been discarded when the load group is unavailable, private channels may remain vulnerable even after a private session has ended. Keeping your software updated and staying informed about the latest vulnerabilities is crucial to safeguarding your privacy and maintaining a secure browsing experience.

Timeline

Published on: 09/11/2023 09:15:00 UTC
Last modified on: 09/14/2023 03:52:00 UTC