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CVE-2026-109739 Mozilla CVE debrief

Mozilla Firefox vulnerability CVE-2026-109739 was published on 2026-10-13T12:29:25.890Z. The vulnerability is a privilege escalation issue in the WebExtensions component, fixed in Firefox 158. This issue allows for potential privilege escalation in Firefox deployments. Defenders should assess exposure and apply the patch to prevent potential privilege escalation. The vulnerability was fixed in Firefox 158, and defenders should prioritize verifying exposure in Firefox deployments and applying the patch.

Vendor
Mozilla
Product
Firefox
CVSS
Unknown
CISA KEV
Not listed in stored evidence
Original CVE published
2026-10-13
Original CVE updated
2026-10-13
Advisory published
2026-10-13
Advisory updated
2026-10-13

Who should care

Defenders responsible for managing Firefox deployments should assess exposure and apply the patch to prevent potential privilege escalation.

Why it matters

CVE-2026-109739 is a privilege escalation vulnerability in the WebExtensions component of Mozilla Firefox. Defenders should prioritize verifying exposure in Firefox deployments and applying the patch to prevent potential privilege escalation. The vulnerability was fixed in Firefox 158.

  • Potential privilege escalation in Firefox WebExtensions component
  • Need to verify exposure and apply patch
  • Possible impact on Firefox deployments

Technical summary

CVE-2026-109739 is a privilege escalation vulnerability in the WebExtensions component of Mozilla Firefox. The issue was fixed in Firefox 158. This vulnerability allows for potential privilege escalation in Firefox deployments, and defenders should prioritize verifying exposure in Firefox deployments and applying the patch to prevent potential privilege escalation. The WebExtensions component is affected, and the vulnerability was fixed in Firefox 158.

Defensive priority

Defenders should prioritize verifying exposure in Firefox deployments and applying the patch to prevent potential privilege escalation.

Recommended defensive actions

  • Verify Firefox version and apply patch if necessary
  • Review WebExtensions component usage and configuration
  • Monitor for potential exploitation attempts

Evidence notes

The CVE record and source item provide limited information about the vulnerability, with the primary details being the existence of a privilege escalation issue in the WebExtensions component of Firefox, fixed in version 158.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-109739 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-109739

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-109739 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-109739

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Privilege escalation in the WebExtensions component

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/109xxx/CVE-2026-109739.json

    cve_program_cvelist_v5

  • Source reference

    Unverified legacy reference

    URL: https://www.mozilla.org/security/advisories/mfsa2026-106/

    Supplemental source

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.