CVE-2026-16383
A critical flaw in Mozilla’s Firefox and Thunderbird browsers allows attackers to bypass security checks in the networking component. The issue was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 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 Mozilla Firefox or Thunderbird, including the ESR (Extended Support Release) editions, are vulnerable.
Real-world impact
An attacker who exploits this flaw can gain complete control over the victim’s system, stealing data, modifying files, and potentially installing malware without the user’s knowledge.
Why this severity
The CVSS score of 9.8 reflects that the vulnerability is reachable over the network, requires no special privileges or user interaction, and compromises confidentiality, integrity, and availability of the affected system.
What to do about it
- 01Upgrade Firefox to version 153 or later.
- 02Upgrade Firefox ESR to version 140.13 or later.
- 03Upgrade Thunderbird to version 153 or later.
- 04Upgrade Thunderbird ESR to version 140.13 or later.
- 05Restart the browsers to apply the updates.
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