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VulnerabilityPublished Updated

CVE-2026-100815: 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
0.2% chance of exploitation in 30 days – higher than 14% 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
Fixed in
  • 153.4
  • 157

AI-suggested

A fix is available and has been released in Firefox ESR 153.4 and Firefox 157. Users and administrators should update to these or later versions to remediate this vulnerability. Refer to Mozilla's security advisories MFSA2026-100 and MFSA2026-97 for official patch details.

Description

CVE-2026-100815 is a use-after-free vulnerability in the CSS Parsing and Computation component of Mozilla Firefox. It allows for potential high impact on confidentiality, integrity, and availability. The issue was fixed in Firefox ESR 153.4 and Firefox 157, as well as Thunderbird 153.4 and 157.

References

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