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VulnerabilityPublished Updated

CVE-2026-100758: Mozilla Firefox · Improper Access Control

Affects Mozilla FirefoxSource CVE Database V5

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Not known to be exploited · CVSS 9.6 Critical · fixed in 153.4 : patch Mozilla Firefox as a priority.

Data as of 13 Nov 2026, 23:53 UTC

CVSS 3.1 base score
9.6Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 23% 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:C/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

Official patches are available and should be applied immediately. Users should upgrade to Firefox ESR 153.4 or later, Firefox 157 or later, Thunderbird 140.17 or later, Thunderbird 153.4 or later, or Thunderbird 157 or later. No additional mitigations are indicated by the vendor advisory.

Description

CVE-2026-100758 is a critical sandbox escape vulnerability in the DOM navigation component of Mozilla Firefox and Thunderbird. It allows an attacker to bypass sandbox restrictions, potentially leading to full compromise of confidentiality, integrity, and availability. The issue has been fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, Firefox ESR 140.17, Thunderbird 140.17, Thunderbird 153.4, and Thunderbird 157.

References

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