Code execution via dangling FontFace pointers
Published Jun 24, 2025 · Updated Apr 13, 2026
Use-after-free in FontFaceSet::Load in Mozilla Firefox and Thunderbird allows remote attackers to execute code via crafted web content. FontFaceSet::Load retains non-refcounted FontFace pointers while promise resolution invokes an attacker-overridden FontFace.prototype.then getter, freeing the objects before f->Load() dereferences them. Affected releases precede Firefox 140, Firefox ESR 115.25 or 128.12 on the respective branches, and Thunderbird 140 or 128.12 on the respective branches; exploitation requires a user to load the script, controlled heap reuse, and an address-disclosure primitive, while the public proof of concept demonstrates a content-process crash.
Summary
What happened
Use-after-free in FontFaceSet::Load in Mozilla Firefox and Thunderbird allows remote attackers to execute code via crafted web content. FontFaceSet::Load retains non-refcounted FontFace pointers while promise resolution invokes an attacker-overridden FontFace.prototype.then getter, freeing the objects before f->Load() dereferences them. Affected releases precede Firefox 140, Firefox ESR 115.25 or 128.12 on the respective branches, and Thunderbird 140 or 128.12 on the respective branches; exploitation requires a user to load the script, controlled heap reuse, and an address-disclosure primitive, while the public proof of concept demonstrates a content-process crash.
The record
- CVE
- CVE-2025-6424
- Published
- Jun 24, 2025
- Updated
- Apr 13, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-416, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 24, 2025CVE publishedPublication date reported by the CVE source.
- Apr 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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What is affected?
Affected products and versions are unavailable in this record.
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- Mozilla Bugzilla crash proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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