Mozilla Firefox and Thunderbird: Mitigation bypass in the Networking HTTP component
Summary
A mitigation bypass in the Networking HTTP component of Mozilla Firefox, Firefox ESR and Thunderbird allows a security protection to be circumvented, as reflected in the CVSS impact rating of high confidentiality and integrity impact. The CVSS vector requires a network attack without privileges, but user interaction is needed, for example by opening crafted web content or mail. Mozilla has not published technical details of the root cause.
Affected
- Mozilla Firefox and Firefox ESR builds older than the fixed releases (exact affected range unknown)
- Mozilla Thunderbird builds older than the fixed releases (exact affected range unknown)
- Vendor-stated fixed releases: Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird 153.5
Fixed in
- Firefox 158 (MFSA 2026-106)
- Firefox ESR 153.5 (MFSA 2026-108)
- Thunderbird 158 (MFSA 2026-109)
- Thunderbird 153.5 (MFSA 2026-110)
- Later releases of the same channel are recommended.
Workaround
Unknown. No vendor workaround has been published. Updating to a fixed release is the remedy.
Exploitation
- Not marked as known exploited in the sources reviewed.
- No public proof of concept found.
- CISA SSVC: Exploitation none, Automatable no, Technical Impact total.
Our recommendation
- Confirm the installed Firefox, Firefox ESR and Thunderbird versions on all endpoints.
- Update to Firefox 158 or Firefox ESR 153.5, and Thunderbird 158 or Thunderbird 153.5, or the latest build of your channel.
- Check managed, pinned and distribution-packaged installs, including Thunderbird on Ubuntu 22.04 LTS.
- Monitor for vendor updates, as the affected version range is not yet confirmed.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Mozilla Security Advisory MFSA 2026-106 (Firefox 158) www.mozilla.org
- Mozilla Security Advisory MFSA 2026-108 (Firefox ESR 153.5) www.mozilla.org
- Mozilla Security Advisory MFSA 2026-109 (Thunderbird 158) www.mozilla.org
- Mozilla Security Advisory MFSA 2026-110 (Thunderbird 153.5) www.mozilla.org
- Bugzilla bug 2070633 bugzilla.mozilla.org
- Ubuntu security notice CVE-2026-109760 ubuntu.com
- Vulners VulnRichment CVE-2026-109760 vulners.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 19:47.
Original description (NVD)
Mitigation bypass in the Networking: HTTP component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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