CVE-2025-26695: Downloading of OpenPGP keys from WKD used incorrect padding

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-03-10 · updated 2026-06-17

Description

When requesting an OpenPGP key from a WKD server, an incorrect padding size was used and a network observer could have learned the length of the requested email address. This vulnerability was fixed in Thunderbird 136 and Thunderbird 128.8.

Affected products

Mozilla Thunderbird: before 128.8.0; from 129.0 before 136.0 — fixed in 128.8.0, 136.0

How to fix

Upgrade to a fixed version: Mozilla Thunderbird 128.8.0, 136.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1883039
https://www.mozilla.org/security/advisories/mfsa2025-17/
https://www.mozilla.org/security/advisories/mfsa2025-18/

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