9.8CRITICAL

CVE-2025-6424 — A use-after-free in FontFaceSet resulted in a potentially exploitable crash.

Mozilla · Firefox · Published 24 Jun 2025 · Modified 30 Sept 2026

Description

A use-after-free in FontFaceSet resulted in a potentially exploitable crash. This vulnerability was fixed in Firefox 140, Firefox ESR 115.25, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1966423
https://www.mozilla.org/security/advisories/mfsa2025-51/
https://www.mozilla.org/security/advisories/mfsa2025-52/
https://www.mozilla.org/security/advisories/mfsa2025-53/
https://www.mozilla.org/security/advisories/mfsa2025-54/
https://www.mozilla.org/security/advisories/mfsa2025-55/
https://lists.debian.org/debian-lts-announce/2025/06/msg00029.html
https://lists.debian.org/debian-lts-announce/2025/07/msg00002.html

What to do

Check whether Firefox is in your asset inventory.
Patch in the next maintenance window; prioritise internet-facing systems.
Record the decision in your risk register for audit evidence.

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Link: adminadda.com/cve/CVE-2025-6424