---
id: CVE-2026-118176
title: 'Bypass of remote UNC path restriction in mailbox: URLs'
summary: >-
  Thunderbird's check that prevents mailbox: URLs from accessing files on remote
  Windows network shares could be bypassed using extended-length UNC paths.
  Displaying a specially crafted email could cause Thunderbird to connect to an
  SMB se…
severity: none
vendor: Mozilla
product: Thunderbird
affected:
  - Thunderbird
published: '2026-10-27'
updated: '2026-10-27'
sourceUpdated: '2026-10-27T18:27:48.875Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-118176'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=2081141'
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-121/'
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-122/'
tags:
  - cve.org
ingestedAt: '2026-10-27T18:52:10.020Z'
---

## Overview

Thunderbird's check that prevents mailbox: URLs from accessing files on remote Windows network shares could be bypassed using extended-length UNC paths. Displaying a specially crafted email could cause Thunderbird to connect to an SMB server chosen by the attacker, disclosing the user's Windows account name and NTLM authentication data, which could be used for offline password cracking or relay attacks.
This bug only affects Thunderbird on Windows. Other operating systems are unaffected. This vulnerability was fixed in Thunderbird 159 and Thunderbird 153.6.

## Affected

- `Thunderbird`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.