What’s Vulnerable › Vulnerabilities

CVE-2023-6856

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 20.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2023-12-19 · updated 2026-06-17
• Weakness: CWE-787

Description

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 Linux: 10.0, 11.0, 12.0
• 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

How to fix

Upgrade to a fixed version: Mozilla Firefox 121.0; Mozilla Firefox ESR 115.6; Mozilla Thunderbird 115.6. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1843782
• https://lists.debian.org/debian-lts-announce/2023/12/msg00020.html
• https://lists.debian.org/debian-lts-announce/2023/12/msg00021.html
• https://security.gentoo.org/glsa/202401-10
• https://www.debian.org/security/2023/dsa-5581
• https://www.debian.org/security/2023/dsa-5582
• https://www.mozilla.org/security/advisories/mfsa2023-54/
• https://www.mozilla.org/security/advisories/mfsa2023-55/
• https://www.mozilla.org/security/advisories/mfsa2023-56/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1843782
• https://lists.debian.org/debian-lts-announce/2023/12/msg00020.html
• https://lists.debian.org/debian-lts-announce/2023/12/msg00021.html

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