CVE-2026-4711: Mozilla Firefox · Use After Free
Affects Mozilla FirefoxSource CVE Database V5
Not known to be exploited · CVSS 9.8 Critical · patch available : patch Mozilla Firefox as a priority.
Data as of 30 Oct 2026, 11:52 UTC
Contested
Critical score, yet low EPSS after six months- EPSS
- 0.4% chance of exploitation in 30 days – higher than 35% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 24 Mar 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 30 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Mozilla Firefox | Affected
| Fixed in
|
AI-suggested
Mozilla has released official fixes for CVE-2026-4711 in Firefox 149 and Firefox ESR 140.9. Users and administrators should update affected Firefox and Thunderbird installations to these versions or later to remediate this vulnerability. Since this is not a cloud service, remediation depends on applying the vendor's patches. There are no vendor advisories indicating that no action is required or that the issue is already mitigated without patching.
Description
Use-after-free in the Widget: Cocoa component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
References
- bugzilla.mozilla.org/show_bug.cgi?id=2017002 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-20/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-22/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-23/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-24/ (opens in a new tab)