CVE-2026-74988 PUBLISHED

Internally found bugs present in Thunderbird ESR 153.0 and Thunderbird 153. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

• Gabriele Svelto, Tom Ritter, Tom Schuster and the Mozilla Fuzzing Team

• Moderate Severity internally found bugs fixed in Thunderbird ESR 153.1 and Thunderbird 154
• High Severity internally found bugs fixed in Thunderbird ESR 153.1 and Thunderbird 154
• Low Severity internally found bugs fixed in Thunderbird ESR 153.1 and Thunderbird 154
• https://www.mozilla.org/security/advisories/mfsa2026-74/
• https://www.mozilla.org/security/advisories/mfsa2026-77/
• https://www.mozilla.org/security/advisories/mfsa2026-78/
• https://www.mozilla.org/security/advisories/mfsa2026-80/