CVE-2026-16396 is a privilege escalation vulnerability affecting the WebExtensions component of Mozilla Firefox. It was resolved in Firefox 153 and Firefox ESR 140.13. This issue is one among many high and moderate impact vulnerabilities fixed in these releases, addressing various security weaknesses including sandbox escapes, use-after-free conditions, information disclosure, and mitigation bypasses. The Mozilla Foundation has published security advisories MFSA2026-68 and MFSA2026-70 detailing these fixes. No active exploitation of CVE-2026-16396 has been reported. The vulnerability allows an attacker to escalate privileges within the browser context, potentially increasing the impact of other attacks.

Successful exploitation of CVE-2026-16396 could allow an attacker to escalate privileges within the Firefox browser environment via the WebExtensions component. This could enable the attacker to perform actions with higher privileges than intended, potentially compromising browser security and user data. However, there are no reports of exploitation in the wild. The vulnerability is part of a larger set of critical and high-impact fixes in Firefox 153 and ESR 140.13 that collectively improve the browser's security posture.

Mozilla has released official fixes for CVE-2026-16396 in Firefox 153 and Firefox ESR 140.13. Users and administrators should update their Firefox installations to these versions or later to remediate this vulnerability. No additional mitigation steps are required beyond applying the official updates.