CVE-2026-100809: Mozilla Firefox · CWE-346
Affects Mozilla FirefoxSource CVE Database V5
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
- 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:NExploitation evidence
Disclosed: evidence found.
CVE published 29 Sep 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 13 Nov 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Mozilla Firefox | Affected
| Fixed in
|
AI-suggested
Mozilla has released official fixes for this vulnerability in Firefox ESR 153.4, Firefox 157, Thunderbird 153.4, and Thunderbird 157. Users and administrators should update to these versions or later to mitigate the risk. Since this is not a cloud service, patching the client software is required. No additional mitigation steps are specified by the vendor.
Description
CVE-2026-100809 is a same-origin policy bypass vulnerability in the DevTools component of Mozilla Firefox. This security flaw allows an attacker to bypass the browser's same-origin policy, potentially leading to unauthorized access to sensitive information. The vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Thunderbird 153.4, and Thunderbird 157. It has a high severity rating with a CVSS score of 8.1. No known exploits are reported in the wild at this time.
References
- bugzilla.mozilla.org/show_bug.cgi?id=2063658 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-100/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-97/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-101/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-103/ (opens in a new tab)