CVE-2020-12406: Canonical Ubuntu Linux

High severity, CVSS 8.8. EPSS: 1% chance of exploitation in the next 30 days.

Mozilla Developer Iain Ireland discovered a missing type check during unboxed objects removal, resulting in a crash. We presume that with enough effort that it could be exploited to run arbitrary code. This vulnerability affects Thunderbird < 68.9.0, Firefox < 77, and Firefox ESR < 68.9.

Affected products

• Canonical Ubuntu Linux: version 16.04 only; version 18.04 only; version 19.10 only; version 20.04 only
• Mozilla Firefox: before 77.0 (fixed in 77.0)
• Mozilla Firefox ESR: before 68.9.0 (fixed in 68.9.0)
• Mozilla Thunderbird: before 68.9.0 (fixed in 68.9.0)

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