CVE-2026-100771: Mozilla Firefox · CWE-758
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 12 Nov 2026, 23:24 UTC
- 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: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
A fix is available. Users and administrators should update affected Mozilla Firefox and Thunderbird versions to the fixed releases: Firefox ESR 153.4 or later, Firefox 157 or later, Firefox ESR 115.42 or later, Firefox ESR 140.17 or later, Thunderbird 140.17 or later, Thunderbird 153.4 or later, and Thunderbird 157 or later. Refer to the official Mozilla security advisories for detailed update instructions.
Description
CVE-2026-100771 is a high severity vulnerability in Mozilla Firefox and Thunderbird involving undefined behavior in the DOM Streams component. This issue affects multiple versions of Firefox and Thunderbird prior to their respective fixed releases. The vulnerability was addressed 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
- bugzilla.mozilla.org/show_bug.cgi?id=2068336 (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/mfsa2026-98/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-99/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-101/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-102/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2026-103/ (opens in a new tab)