Use-after-free in the DOM: Core & HTML component

A use-after-free vulnerability occurs when a program attempts to access memory that has already been freed. In the context of Firefox, this could allow an attacker to craft a malicious web page that, when visited by a user, triggers the vulnerability. Successful exploitation could lead to a denial-of-service (DoS) by crashing the browser, or, more seriously, allow the attacker to execute arbitrary code within the context of the user's browser session. This could enable the attacker to steal sensitive data, install malware, or take control of the user's system. The impact is amplified if the user has elevated privileges or access to sensitive information.

Users of Firefox and Thunderbird within the affected version range (115.0.0–140.*) are at risk. This includes individuals, businesses, and organizations that rely on these browsers for web browsing and email communication. Users who frequently visit untrusted websites or download files from unknown sources are at higher risk.

• firefox: Monitor Firefox process memory for unexpected crashes or errors related to memory allocation. Use memory debugging tools to identify potential use-after-free conditions. • generic web: Inspect browser console for JavaScript errors related to memory access. Analyze network traffic for suspicious requests or responses. • linux / server: Use tools like Valgrind to profile Firefox's memory usage and detect memory errors during runtime. Examine system logs for crash reports or unusual activity related to Firefox.

1. 2026-04-21Disclosure

   disclosure

1. 予約済み2026-04-21
2. 公開日2026-04-21
3. 更新日2026-04-22
4. EPSS 更新日2026-04-29

The primary mitigation for CVE-2026-6746 is to upgrade to a patched version of Firefox or Thunderbird. Specifically, upgrade to Firefox 150.0.0 or later, Firefox ESR 115.35 or later, Firefox ESR 140.10 or later, Thunderbird 150 or later, or Thunderbird 140.10 or later. If immediate upgrading is not possible, consider implementing stricter content security policies (CSP) to limit the potential attack surface. While not a direct fix, CSP can restrict the resources a page can load, potentially hindering exploitation. Monitor network traffic for unusual patterns or connections that might indicate exploitation attempts. After upgrading, confirm the fix by visiting a known safe website and verifying that the browser version reflects the patched version.