CVE-2026-6763 is a mitigation bypass vulnerability affecting the File Handling component in Mozilla Firefox. It allows an attacker to bypass security mitigations, potentially weakening the browser's defense mechanisms related to file operations. The issue was fixed in Firefox 150 and Firefox ESR 140.10, as well as Thunderbird 150 and Thunderbird 140.10. The CVSS 3.1 base score is 6.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N), indicating that the vulnerability is remotely exploitable without privileges or user interaction and can lead to low confidentiality and integrity impacts without affecting availability.

The vulnerability could allow an attacker to bypass mitigation controls in the File Handling component, potentially leading to unauthorized access or manipulation of files within the browser context. The impact is rated as medium with confidentiality and integrity impacts but no availability impact. There are no known exploits in the wild, reducing immediate risk.

This vulnerability has been fixed in Mozilla Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10. Users and administrators should update to these versions or later to remediate the issue. Since the vendor advisory confirms the fix, no additional mitigation steps are required beyond applying the official update.