CVE-2026-100794: Mozilla Thunderbird · Memory Buffer Overflow
Affects Mozilla ThunderbirdSource CVE Database V5
Not known to be exploited · CVSS 9.6 Critical · fixed in 140.17 : patch Mozilla Thunderbird as a priority.
Data as of 13 Nov 2026, 23:53 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 25% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 140.17
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 29 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.
What to do
AI-suggested
This vulnerability has been fixed by Mozilla. Users should update to Thunderbird versions 140.17, 153.4, or 157, or the corresponding Firefox ESR versions 140.17, 153.4, or Firefox 157 to mitigate this issue. Applying these official fixes eliminates the vulnerability.
Description
CVE-2026-100794 is a critical vulnerability in Mozilla Thunderbird involving a sandbox escape caused by incorrect boundary conditions in the Internationalization component. This flaw allows an attacker to bypass sandbox protections, potentially leading to full compromise of confidentiality, integrity, and availability. The issue has been fixed in Thunderbird versions 140.17, 153.4, and 157, as well as Firefox ESR 140.17, ESR 153.4, and Firefox 157.
References
- bugzilla.mozilla.org/show_bug.cgi?id=2028871 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-100/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-97/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-99/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-101/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-102/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-103/ (opens in a new tab)