CVE-2021-43535: Debian Linux

High severity, CVSS 8.8. EPSS: 1.1% chance of exploitation in the next 30 days.

A use-after-free could have occured when an HTTP2 session object was released on a different thread, leading to memory corruption and a potentially exploitable crash. This vulnerability affects Firefox < 93, Thunderbird < 91.3, and Firefox ESR < 91.3.

Affected products

• Debian Debian Linux: version 9.0 only; version 10.0 only; version 11.0 only
• Mozilla Firefox: before 93.0 (fixed in 93.0)
• Mozilla Firefox ESR: before 91.3.0 (fixed in 91.3.0)
• Mozilla Thunderbird: before 91.3.0 (fixed in 91.3.0)

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