Executive brief
A security vulnerability has been identified in the Mozilla Firefox web browser that could allow a malicious website to bypass the browser's security sandbox. The sandbox is a critical defense layer designed to prevent malicious code from interacting with the rest of your computer. If successfully exploited, an attacker could potentially gain unauthorized access to your system or data beyond the browser's normal limits. Users should update to the latest versions of Firefox to protect their systems.
Technical details
A sandbox escape vulnerability exists in Mozilla Firefox and Firefox ESR due to incorrect boundary conditions within the 'Widget: Win32' component. The flaw allows an attacker to bypass the process sandboxing protections that normally isolate the browser's content process from the underlying operating system. While specific exploitation details are restricted in the associated bug report (Bug 2034754), sandbox escapes typically require a secondary vulnerability, such as remote code execution (RCE), to be triggered from a compromised content process. This issue was addressed by improving boundary checks in the Win32 widget handling code. Fixed versions include Firefox 151 and Firefox ESR 140.11.
Affected products
- Mozilla Firefox < 151
- Mozilla Firefox ESR < 140.11
Timeline
- 2026-05-19: disclosed
- 2026-05-19: patched
- 2026-05-19: advisory