CVE-2026-92238: Ambiguous parsing of mail headers

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-15 · updated 2026-09-24
Weakness: CWE-444

Description

A maliciously constructed mail header could lead to multiple fields being parsed as one, or potential memory safety violations. This vulnerability was fixed in Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3.

Affected products

Mozilla Thunderbird: before 140.16.0; from 141.0 before 153.3.0; from 154.0 before 156.0 — fixed in 140.16.0, 153.3.0, 156.0

How to fix

Upgrade to a fixed version: Mozilla Thunderbird 140.16.0, 153.3.0, 156.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2060601
https://www.mozilla.org/security/advisories/mfsa2026-94/
https://www.mozilla.org/security/advisories/mfsa2026-95/
https://www.mozilla.org/security/advisories/mfsa2026-96/

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