CVE-2021-23993

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-06-24 · updated 2026-06-17
Weakness: CWE-347

Description

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.

Affected products

Mozilla Thunderbird: before 78.9.1 — fixed in 78.9.1

How to fix

Upgrade to a fixed version: Mozilla Thunderbird 78.9.1. Check the vendor advisory for mitigations.

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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