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9.8
Firefox and Thunderbird: Privilege Escalation Risk from Messaging System
CVE-2026-2777
Summary
Mozilla's Firefox and Thunderbird browsers have a security weakness that could allow an attacker to take control of your system. This affects older versions of these browsers, which means it's essential to update to the latest versions to protect your computer and sensitive information.
What to do
No fix is available yet. Check with your software vendor for updates.
Affected software
| Vendor | Product | Affected versions | Fix available |
|---|---|---|---|
| mozilla | firefox | <= 115.33.0 | – |
| mozilla | firefox | <= 148.0 | – |
| mozilla | firefox | > 128.0 , <= 140.8.0 | – |
| mozilla | thunderbird | <= 140.8.0 | – |
| mozilla | thunderbird | <= 148.0 | – |
Original title
Privilege escalation in the Messaging System component. This vulnerability affects Firefox < 148, Firefox ESR < 115.33, Firefox ESR < 140.8, Thunderbird < 148, and Thunderbird < 140.8.
Original description
Privilege escalation in the Messaging System component. This vulnerability affects Firefox < 148, Firefox ESR < 115.33, Firefox ESR < 140.8, Thunderbird < 148, and Thunderbird < 140.8.
nvd CVSS3.1
9.8
Vulnerability type
CWE-269
Improper Privilege Management
- https://bugzilla.mozilla.org/show_bug.cgi?id=2015305 Issue Tracking Permissions Required
- https://www.mozilla.org/security/advisories/mfsa2026-13/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-14/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-15/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-16/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-17/ Vendor Advisory
Published: 24 Feb 2026 · Updated: 12 Mar 2026 · First seen: 6 Mar 2026