CVE-2026-100757: Use After Free
Source GCVE Database
Not known to be exploited · CVSS 8.8 High · fixed in 153.4 : patch Firefox soon.
Data as of 12 Nov 2026, 23:24 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 25% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 153.4
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
AI-suggested
This vulnerability has been fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17. Users and administrators should update to these versions or later to remediate the issue. No additional mitigation steps are required beyond applying the official patches.
Description
CVE-2026-100757 is a use-after-free vulnerability in the Widget component of Firefox. It was fixed in Firefox ESR versions 153.4, 157, 115.42, and 140.17. The vulnerability has a high severity rating with a CVSS score of 8.8, indicating it can lead to significant confidentiality, integrity, and availability impacts. No known exploits in the wild have been reported.
References
- nvd.nist.gov/vuln/detail/CVE-2026-100757 (opens in a new tab)
- bugzilla.mozilla.org/show_bug.cgi?id=2049352 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-100 (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)
- 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)