Skip to main content
A Leader in the 2026 Gartner® Magic Quadrant™ for Endpoint Protection. Six years running.Find Out Why
Vulnerability Database/CVE-2026-109747

CVE-2026-109747: Firefox Address Bar Security Vulnerability

CVE-2026-109747 is a security flaw affecting the Address Bar component in Firefox and Thunderbird browsers. This issue was resolved in version 158 of both applications. This post covers technical details, affected versions, security impact, and mitigation steps.

Published:

CVE-2026-109747 Overview

CVE-2026-109747 is a vulnerability in the Address Bar component of Mozilla Firefox and Thunderbird. Mozilla documented the issue in security advisories MFSA 2026-106 and MFSA 2026-109. The flaw was corrected in Firefox 158 and Thunderbird 158.

Mozilla classified the problem as an "Other issue" within the Address Bar, which handles URL display and user navigation input. Address Bar flaws commonly enable spoofing scenarios that mislead users about the origin of displayed content. Mozilla has not published a CVSS vector, CWE identifier, or detailed technical description for this entry.

Critical Impact

Users running Firefox or Thunderbird versions earlier than 158 remain exposed to an unspecified Address Bar defect that may undermine the trust indicators users rely on to validate web content.

Affected Products

  • Mozilla Firefox versions prior to 158
  • Mozilla Thunderbird versions prior to 158
  • Any downstream distributions bundling the affected Gecko engine versions

Discovery Timeline

  • 2026-10-13 - CVE-2026-109747 published to the National Vulnerability Database (NVD)
  • 2026-10-13 - Last updated in NVD database

Technical Details for CVE-2026-109747

Vulnerability Analysis

Mozilla's advisory lists the issue as an "Other issue in the Address Bar component." The Address Bar is the browser surface responsible for parsing, normalizing, and displaying URLs. Defects in this component typically fall into spoofing, origin confusion, or input-handling categories.

Mozilla patched the condition in Firefox 158 and in Thunderbird 158, which shares Gecko platform code with Firefox. Thunderbird is affected because it uses the same URL rendering stack when previewing message content and handling links. The vendor has not published a CWE classification or exploitation prerequisites for this record.

Root Cause

Mozilla has not disclosed the specific root cause in the public NVD entry. The linked Bugzilla report (Mozilla Bug 2065402) remains the authoritative source for technical details once Mozilla opens it to the public.

Attack Vector

The attack vector is not formally scored. Address Bar vulnerabilities typically require a victim to visit an attacker-controlled page or open a crafted link in an email client. For Thunderbird, exposure extends to message preview and URL hover scenarios. Refer to Mozilla Security Advisory MFSA 2026-106 and Mozilla Security Advisory MFSA 2026-109 for the vendor's full description.

No verified proof-of-concept code is published for this CVE. See the referenced advisories for authoritative technical commentary.

Detection Methods for CVE-2026-109747

Indicators of Compromise

  • No vendor-published indicators of compromise are available for CVE-2026-109747.
  • Monitor browser telemetry for unexpected URL rendering anomalies reported by end users.
  • Track Firefox and Thunderbird version strings reported by endpoints against the fixed baseline of 158.

Detection Strategies

  • Inventory installed Firefox and Thunderbird builds across managed endpoints and flag versions earlier than 158.
  • Correlate browser user-agent strings observed in web proxy or email gateway logs to identify unpatched clients.
  • Review phishing and credential-theft alerts for cases where victims report confusion about displayed URLs.

Monitoring Recommendations

  • Subscribe to Mozilla Foundation Security Advisories to receive updates on related Gecko fixes.
  • Monitor Bugzilla entry 2065402 for public technical disclosure once Mozilla lifts the embargo.
  • Alert on execution of outdated firefox.exe or thunderbird.exe binaries on managed systems.

How to Mitigate CVE-2026-109747

Immediate Actions Required

  • Upgrade Firefox to version 158 or later across all managed endpoints.
  • Upgrade Thunderbird to version 158 or later on all workstations handling email.
  • Verify that automatic updates are enabled for both products in enterprise policy.
  • Validate that Extended Support Release (ESR) channels receive the corresponding fix before the next maintenance window.

Patch Information

Mozilla released fixes in Firefox 158 and Thunderbird 158. Consult Mozilla Security Advisory MFSA 2026-106 and Mozilla Security Advisory MFSA 2026-109 for the full list of CVEs addressed in these releases. Downstream Linux distributions should apply the vendor-packaged updates as they become available.

Workarounds

  • No vendor-supplied workaround is documented for this CVE.
  • Users should visually verify the displayed URL before entering credentials on sensitive sites.
  • Enterprises can restrict access to untrusted sites via web proxy policy until patches are deployed.
bash
# Verify installed Firefox version on Linux endpoints
firefox --version

# Verify installed Thunderbird version on Linux endpoints
thunderbird --version

# Example Windows version check via PowerShell
(Get-Item "C:\Program Files\Mozilla Firefox\firefox.exe").VersionInfo.ProductVersion

Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.

Experience the Most Advanced Cybersecurity Platform

See how the world’s most intelligent, autonomous cybersecurity platform can protect your organization today and into the future.

Try SentinelOne