Executive brief
A security vulnerability has been identified in the PDF Viewer component of the Firefox web browser. This flaw allows an attacker to bypass certain security mitigations designed to protect the user. Exploiting this could weaken the browser's overall security posture when viewing malicious PDF documents, though it does not directly lead to data theft or system takeover on its own.
Technical details
A mitigation bypass vulnerability exists in the PDF Viewer component of Mozilla Firefox. The flaw allows for the circumvention of built-in security mitigations, which are typically intended to restrict the capabilities of untrusted content. The vulnerability is reachable via the network if a user is persuaded to open a malicious PDF document. While the specific technical root cause is not detailed in the advisory, it is classified as a 'moderate' impact issue by Mozilla. The vulnerability is addressed in Firefox 153 and Firefox ESR 140.13.
Affected products
- Mozilla Firefox Before 153
- Mozilla Firefox ESR Before 140.13
Timeline
- 2026-07-21: advisory
- 2026-07-21: disclosed
- 2026-07-21: patched