CVE-2026-100784: Mozilla Firefox · Use After Free
Affects Mozilla FirefoxSource CVE Database V5
Not known to be exploited · CVSS 8.8 High.
Data as of 12 Nov 2026, 23:24 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 26% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 29 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Mozilla Firefox | Affected
| Fixed in
|
AI-suggested
Mozilla has released official fixes for this vulnerability in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, Firefox ESR 140.17, Thunderbird 157, Thunderbird 140.17, and Thunderbird 153.4. Users and administrators should update to these fixed versions to remediate the vulnerability. No additional mitigation steps are required beyond applying these official updates.
Description
CVE-2026-100784 is a use-after-free vulnerability in the Layout: Text and Fonts component of Mozilla Firefox and Thunderbird. It affects multiple versions of Firefox and Thunderbird prior to their respective fixed releases. The vulnerability has a high severity with a CVSS score of 8.8, indicating it can lead to significant confidentiality, integrity, and availability impacts. Mozilla has released official fixes in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, Firefox ESR 140.17, Thunderbird 157, Thunderbird 140.17, and Thunderbird 153.4.
References
- bugzilla.mozilla.org/show_bug.cgi?id=2070264 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-100/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-97/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-98/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-99/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-101/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-102/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-103/ (opens in a new tab)