CVE-2023-6859

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% 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-416

Description

A use-after-free condition affected TLS socket creation when under memory pressure. 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=1840144
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=1840144
https://lists.debian.org/debian-lts-announce/2023/12/msg00020.html
https://lists.debian.org/debian-lts-announce/2023/12/msg00021.html

Get alerted when CVE-2023-6859 or the next vulnerability affects your stack