CVE-2020-26971: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 1.9% chance of exploitation in the next 30 days.

Certain blit values provided by the user were not properly constrained leading to a heap buffer overflow on some video drivers. This vulnerability affects Firefox < 84, Thunderbird < 78.6, and Firefox ESR < 78.6.

Affected products

• Mozilla Firefox: before 84.0 (fixed in 84.0)
• Mozilla Firefox ESR: before 78.6.0 (fixed in 78.6.0)
• Mozilla Thunderbird: before 78.6.0 (fixed in 78.6.0)

Published 2021-01-07. Last modified 2026-06-17.