CVE-2020-12421: Canonical Ubuntu Linux

Medium severity, CVSS 6.5. EPSS: 1.8% chance of exploitation in the next 30 days.

When performing add-on updates, certificate chains terminating in non-built-in-roots were rejected (even if they were legitimately added by an administrator.) This could have caused add-ons to become out-of-date silently without notification to the user. This vulnerability affects Firefox ESR < 68.10, Firefox < 78, and Thunderbird < 68.10.0.

Affected products

• Canonical Ubuntu Linux: version 16.04 only; version 18.04 only; version 19.10 only; version 20.04 only
• Mozilla Firefox: before 78.0 (fixed in 78.0)
• Mozilla Firefox ESR: before 68.10.0 (fixed in 68.10.0)
• Mozilla Thunderbird: before 68.10.0 (fixed in 68.10.0)

Published 2020-07-09. Last modified 2026-06-17.