Mozilla Firefox: Privilege escalation in the DOM Navigation component
Summary
Mozilla Firefox, Firefox ESR and Thunderbird contain a privilege escalation flaw in the DOM Navigation component. According to the CVSS vector, an attacker can act remotely with low complexity and no privileges, but the user must interact, typically by visiting a malicious or compromised web page. Successful exploitation could affect confidentiality, integrity and availability, and CISA SSVC rates the technical impact as total.
Affected
- Mozilla Firefox and Firefox ESR releases before 158 and 153.5 respectively (per the CNA's unaffected ranges)
- Mozilla Thunderbird releases before 158 and 153.5 (per the CNA record; the Thunderbird fix is not confirmed by a primary source)
- Debian firefox-esr: fixed in 153.5.0esr-1~deb12u1 (bookworm)
- Ubuntu thunderbird on 22.04 LTS (jammy): marked vulnerable
Fixed in
- Firefox 158
- Firefox ESR 153.5
- Thunderbird 158 and Thunderbird 153.5 (per the CVE description; not independently verified)
- Debian firefox-esr 153.5.0esr-1~deb12u1 (bookworm)
Workaround
Unknown. No workaround is documented in the available sources; the fix is the update.
Exploitation
- Not listed as known exploited (not in CISA KEV)
- EPSS: 0.00323
- CISA SSVC: Exploitation none, Automatable no, Technical Impact total
- No public proof of concept found in the searches performed; this does not rule out that one exists
Our recommendation
- Update all Firefox, Firefox ESR and Thunderbird installations to the fixed versions without delay, prioritising endpoints that browse untrusted content
- Check which release channel is in use (Firefox or ESR) and verify the installed version
- Verify the Thunderbird version against Mozilla's advisories MFSA 2026-109 and 2026-110
- Monitor for public exploit code or a KEV listing
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Mozilla Bugzilla bug 2069258 bugzilla.mozilla.org
- Mozilla MFSA 2026-106 (Firefox 158) www.mozilla.org
- Mozilla MFSA 2026-108 (Firefox ESR 153.5) www.mozilla.org
- Mozilla MFSA 2026-109 (Thunderbird 158) www.mozilla.org
- Mozilla MFSA 2026-110 (Thunderbird 153.5) www.mozilla.org
- Ubuntu security notice CVE-2026-109756 ubuntu.com
- Debian OSV entry CVE-2026-109756 osv.dev
- Vulmon CVE-2026-109756 vulmon.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 31 Oct 2026, 20:11.
Original description (NVD)
Privilege escalation in the DOM: Navigation 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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