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VulnerabilityPublished Updated

CVE-2026-100816: Mozilla Firefox · CWE-346

Affects Mozilla FirefoxSource CVE Database V5

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Not known to be exploited · CVSS 8.1 High · fixed in 153.4 : patch Mozilla Firefox soon.

Data as of 13 Nov 2026, 23:53 UTC

CVSS 3.1 base score
8.1High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 4% 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:N

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

Official patches are available from Mozilla. Users should update to Firefox ESR 153.4 or Firefox 157 or later to remediate this vulnerability. Thunderbird users should similarly update to versions 153.4 or 157 or later. No additional mitigation steps are indicated by the vendor advisories.

Description

CVE-2026-100816 is a high-severity vulnerability in Mozilla Firefox related to a site isolation issue in the DOM networking component. It allows potential compromise of confidentiality and integrity but does not affect availability. The flaw was fixed in Firefox ESR 153.4 and Firefox 157, as well as Thunderbird 153.4 and 157.

References

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