CVE-2026-16351
A use‑after‑free bug in Firefox and Thunderbird lets attackers escape the browser sandbox, potentially running arbitrary code on the host. The flaw was fixed in Firefox 153 and ESR 115.38/140.13, and in Thunderbird 153 and ESR 140.13.
An official fix is available, so this entry is kept for 30 days and then removed automatically.
Who is affected
Users running older versions of Firefox or Thunderbird before the fixed releases (Firefox <153, ESR 115.38/140.13; Thunderbird <153, ESR 140.13).
Real-world impact
An attacker could break out of the browser sandbox and execute code with the privileges of the user, leading to full system compromise.
Why this severity
The CVSS score of 9.8 reflects that the vulnerability allows complete compromise without authentication, with no user interaction required, and affects confidentiality, integrity, and availability.
What to do about it
- 011. Update Firefox to version 153 or later, or to ESR 115.38 or later.
- 022. Update Thunderbird to version 153 or later, or to ESR 140.13 or later.
NVD-referenced vendor advisory
Timeline
- Jul 21, 2026 · 12d agoPublishedDisclosed and added to the National Vulnerability Database.
- Jul 23, 2026 · 10d agoOfficial fix availableA vendor patch or mitigation now exists — see the remediation steps above.
- Jul 24, 2026 · 9d agoAdvisory updatedThe NVD record was last revised.
How it’s attacked
References & advisories
- bugzilla.mozilla.org/show_bug.cgipermissions required
- mozilla.org/security/advisories/mfsa202…vendor advisory
- mozilla.org/security/advisories/mfsa202…vendor advisory
- mozilla.org/security/advisories/mfsa202…vendor advisory
- mozilla.org/security/advisories/mfsa202…vendor advisory
- mozilla.org/security/advisories/mfsa202…vendor advisory