CVE-2021-43539: Debian Linux

High severity, CVSS 8.8. EPSS: 1.7% chance of exploitation in the next 30 days.

Failure to correctly record the location of live pointers across wasm instance calls resulted in a GC occurring within the call not tracing those live pointers. This could have led to a use-after-free causing a potentially exploitable crash. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

Affected products

• Debian Debian Linux: version 9.0 only; version 10.0 only; version 11.0 only
• Mozilla Firefox: before 95.0 (fixed in 95.0)
• Mozilla Firefox ESR: before 91.4.0 (fixed in 91.4.0)
• Mozilla Thunderbird: before 91.4.0 (fixed in 91.4.0)

Published 2021-12-08. Last modified 2026-06-17.