CVE-2021-4126

6.5 mediumEPSS 0.5%

Medium (6.5) in mozilla thunderbird. EPSS 0.5% chance of exploitation in the next 30 days.

When receiving an OpenPGP/MIME signed email message that contains an additional outer MIME message layer, for example a message footer added by a mailing list gateway, Thunderbird only considered the inner signed message for the signature validity. This gave the false impression that the additional contents were also covered by the digital signature. Starting with Thunderbird version 91.4.1, only the signature that belongs to the top level MIME part will be considered for the displayed status. This vulnerability affects Thunderbird < 91.4.1.

Severity

CVSS 3.1

6.5 medium

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

EPSS: 0.5% chance of exploitation in the next 30 days; higher than 39% of CVEs (scores of 2026-10-31)
Published: 2022-12-22
Modified: 2026-06-17
Record from: the NVD, synced 2026-10-19

Affected

mozilla:thunderbird

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1732310
https://www.mozilla.org/security/advisories/mfsa2021-55/
https://bugzilla.mozilla.org/show_bug.cgi?id=1732310
https://www.mozilla.org/security/advisories/mfsa2021-55/

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