CVE-2021-38501: Mozilla Firefox

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

Mozilla developers reported memory safety bugs present in Firefox 92 and Firefox ESR 91.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 93, Thunderbird < 91.2, and Firefox ESR < 91.2.

Affected products

• Mozilla Firefox: before 93.0 (fixed in 93.0)
• Mozilla Firefox ESR: before 91.2 (fixed in 91.2)
• Mozilla Thunderbird: before 91.2 (fixed in 91.2)

Published 2021-11-03. Last modified 2026-06-17.