CVE-2020-15656: Canonical Ubuntu Linux

High severity, CVSS 8.8. EPSS: 1.5% chance of exploitation in the next 30 days.

JIT optimizations involving the Javascript arguments object could confuse later optimizations. This risk was already mitigated by various precautions in the code, resulting in this bug rated at only moderate severity. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1.

Affected products

• Canonical Ubuntu Linux: version 16.04 only; version 18.04 only; version 20.04 only
• Mozilla Firefox: before 79.0 (fixed in 79.0)
• Mozilla Firefox ESR: before 78.1 (fixed in 78.1)
• Mozilla Thunderbird: before 78.1 (fixed in 78.1)
• Opensuse Leap: version 15.2 only

Published 2020-08-10. Last modified 2026-06-17.