CVE-2021-23993

6.5 mediumEPSS 0.4%

Medium (6.5) in mozilla thunderbird. EPSS 0.4% chance of exploitation in the next 30 days.

An attacker may perform a DoS attack to prevent a user from sending encrypted email to a correspondent. If an attacker creates a crafted OpenPGP key with a subkey that has an invalid self signature, and the Thunderbird user imports the crafted key, then Thunderbird may try to use the invalid subkey, but the RNP library rejects it from being used, causing encryption to fail. This vulnerability affects Thunderbird < 78.9.1.

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: 0.4% chance of exploitation in the next 30 days; higher than 36% of CVEs (scores of 2026-10-31)
CWE: CWE-347
Published: 2021-06-24
Modified: 2026-06-17
Record from: the NVD, synced 2026-10-19

Affected

mozilla:thunderbird

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1666360
https://www.mozilla.org/security/advisories/mfsa2021-13/
https://bugzilla.mozilla.org/show_bug.cgi?id=1666360
https://www.mozilla.org/security/advisories/mfsa2021-13/

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