CVE-2023-6856: Debian Linux

High severity, CVSS 8.8. EPSS: 20.6% chance of exploitation in the next 30 days.

The WebGL `DrawElementsInstanced` method was susceptible to a heap buffer overflow when used on systems with the Mesa VM driver. This issue could allow an attacker to perform remote code execution and sandbox escape. This vulnerability affects Firefox ESR < 115.6, Thunderbird < 115.6, and Firefox < 121.

Affected products

• Debian Debian Linux: version 10.0 only; version 11.0 only; version 12.0 only
• Mozilla Firefox: before 121.0 (fixed in 121.0)
• Mozilla Firefox ESR: before 115.6 (fixed in 115.6)
• Mozilla Thunderbird: before 115.6 (fixed in 115.6)

Published 2023-12-19. Last modified 2026-06-17.