CVE-2026-16405: 
NixOS vulnerability analysis and mitigation

CVE-2026-16405 is an information disclosure vulnerability in the Networking: WebSockets component of Mozilla Firefox and Firefox ESR. Discovered and reported by Yaqoub Aldurayhim, it was publicly disclosed on July 21, 2026, as part of Mozilla's coordinated security advisory release. Affected versions include Firefox prior to 153 and Firefox ESR prior to 140.13. Mozilla rates the impact as low, and no CVSS score has been formally assigned at the time of this report (Mozilla Advisory mfsa2026-68, Mozilla Advisory mfsa2026-70).

The vulnerability resides in Firefox's Networking: WebSockets component and results in unintended information disclosure. The specific root cause (CWE classification) has not been publicly detailed, as the associated Bugzilla report (Bug 2036591) is access-restricted. Based on the advisory classification, the flaw likely involves improper handling or exposure of sensitive data during WebSocket communication, potentially allowing a web-based attacker to read information they should not have access to. No public technical write-ups or proof-of-concept code have been identified at this time (Mozilla Advisory mfsa2026-68, Mozilla Advisory mfsa2026-70).

Successful exploitation of this vulnerability results in unauthorized information disclosure through the WebSockets networking layer in Firefox. The confidentiality impact is limited in scope — integrity and availability are not affected. Given the low severity rating assigned by Mozilla, the data exposed is likely constrained in sensitivity, but could still be leveraged in targeted attacks or combined with other vulnerabilities for greater effect (Mozilla Advisory mfsa2026-68, Mozilla Advisory mfsa2026-70).

Mozilla has released patches addressing this vulnerability. Users should upgrade to Firefox 153 or Firefox ESR 140.13 or later. No configuration-based workarounds have been published. Organizations using Firefox in enterprise environments should prioritize updating via their standard patch management processes, particularly given the broader set of higher-severity vulnerabilities addressed in the same advisory cycle (Mozilla Advisory mfsa2026-68, Mozilla Advisory mfsa2026-70).