CVE-2026-16381
A critical flaw in Firefox and Thunderbird lets attackers bypass the same-origin policy in the DNS component, potentially exposing sensitive data. The vulnerability can be exploited over the network without any user interaction or special privileges. Updating to the latest versions removes the risk.
An official fix is available, so this entry is kept for 30 days and then removed automatically.
Who is affected
Firefox and Thunderbird browsers, including their ESR releases, on any platform where the affected versions are installed.
Real-world impact
An attacker could read or modify data that should be protected by the same-origin policy, potentially accessing sensitive information or injecting malicious content. This could lead to data theft or compromise of user sessions.
Why this severity
The CVSS score of 9.1 indicates a high risk because the flaw can be exploited remotely over the network, requires no privileges or user interaction, and can compromise confidentiality and integrity of data, though it does not affect availability.
What to do about it
- 01Upgrade Firefox to version 153 or later.
- 02Upgrade Firefox ESR to 140.13 or later.
- 03Upgrade Thunderbird to version 153 or later.
- 04Upgrade Thunderbird ESR to 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