Thunderbird <159 Windows extended UNC bypass (NTLM leak)
CVE-2026-118176 Published on October 27, 2026

Bypass of remote UNC path restriction in mailbox: URLs
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.

NVD

Vulnerability Analysis

CVE-2026-118176 is exploitable with network access, requires user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a high impact on confidentiality and integrity, and no impact on availability.

Exploitation:
NONE
Automatable:
NO
Technical Impact:
TOTAL
Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
REQUIRED
Scope:
UNCHANGED
Confidentiality Impact:
HIGH
Integrity Impact:
HIGH
Availability Impact:
NONE

Weakness Type

What is an Information Disclosure Vulnerability?

The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.

CVE-2026-118176 has been classified to as an Information Disclosure vulnerability or weakness.


Products Associated with CVE-2026-118176

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Mozilla Thunderbird

Affected Versions

Mozilla Thunderbird: