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VulnerabilityPublished Updated

CVE-2026-100767: Mozilla Firefox · Use After Free

Affects Mozilla FirefoxSource CVE Database V5

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Not known to be exploited · CVSS 8.8 High · fixed in 153.4 : patch Mozilla Firefox soon.

Data as of 12 Nov 2026, 23:24 UTC

CVSS 3.1 base score
8.8High
How severe the flaw is on the 0–10 CVSS scale.
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.
Patch
Available – fixed in 153.4
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 29 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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

ProductAffectedFixed in
Mozilla FirefoxAffected
  • <153.4
  • <157
  • <115.42
  • <140.17
Fixed in
  • 153.4
  • 157
  • 115.42
  • 140.17

AI-suggested

This vulnerability has been fixed by Mozilla 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 versions or later to remediate the vulnerability. No additional mitigation steps are indicated by the vendor advisories.

Description

CVE-2026-100767 is a use-after-free vulnerability in the Networking: Cache component of Mozilla Firefox and Thunderbird. This vulnerability allows for potential remote code execution or other impacts due to improper memory handling. It affects multiple versions of Firefox and Thunderbird prior to their respective fixed releases. The vulnerability has a high severity score of 8.8 and was fixed 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

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