CVE-2026-74983 is a mitigation bypass vulnerability affecting the Data Loss Prevention component in Mozilla Firefox. The flaw allows bypassing security mitigations designed to prevent data loss, potentially weakening the protection mechanisms. Mozilla fixed this vulnerability in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1 as part of a comprehensive security update that addressed multiple high-impact vulnerabilities. The advisory notes that these bugs were internally discovered and some could have been exploitable with sufficient effort. No active exploitation has been reported.

The vulnerability could allow an attacker to bypass mitigation controls in the Data Loss Prevention component, potentially leading to unauthorized data exposure or loss. However, the impact is considered low relative to other high-impact vulnerabilities fixed in the same release. There are no reports of active exploitation in the wild. The fix eliminates the risk by restoring the intended mitigation effectiveness.

Mozilla has released official fixes for this vulnerability in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1. Users and administrators should update to these versions or later to remediate the issue. Since the vulnerability is fixed in these versions, no additional mitigation steps are required beyond applying the update.