Mozilla Firefox and Thunderbird: Same-origin policy bypass in DevTools component
Summary
Mozilla Firefox and Thunderbird contain a same-origin policy bypass in the DevTools component. Per the CVSS vector, an attacker can reach high confidentiality and integrity impact over the network without privileges or user interaction. Mozilla's advisory rates the overall impact as high, and CISA SSVC lists exploitation as none. Further exploitation conditions are unknown.
Affected
- Mozilla Firefox versions before 158 (exact range not confirmed by Mozilla in available sources)
- Mozilla Thunderbird versions before 158 (exact range not confirmed by Mozilla in available sources)
- NVD status: Deferred
Fixed in
- Mozilla Firefox 158
- Mozilla Thunderbird 158
Workaround
Unknown.
Exploitation
- No public exploitation reported in the sources reviewed.
- CISA SSVC: Exploitation none, Automatable yes, Technical Impact total.
Our recommendation
- Update Firefox and Thunderbird to version 158 or later on all systems.
- Check for older browser or mail client installations, including managed and portable installs.
- Monitor Mozilla advisories for updates on this CVE.
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 2026-109 (Thunderbird 158) www.mozilla.org
- Ubuntu Security Notice CVE-2026-109772 ubuntu.com
- Mozilla Bugzilla bug 2066063 bugzilla.mozilla.org
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 31 Oct 2026, 06:50.
Original description (NVD)
Same-origin policy bypass in the DevTools component. This vulnerability was fixed in Firefox 158 and Thunderbird 158.
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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