CVE-2021-23993: Mozilla Thunderbird

Medium severity, CVSS 6.5. 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.

Affected products

• Mozilla Thunderbird: before 78.9.1 (fixed in 78.9.1)

Published 2021-06-24. Last modified 2026-06-17.