CVE-2026-118176: Bypass of remote UNC path restriction in mailbox: URLs

Published Oct 27, 2026
·
Updated

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.

Affected Software

2 affected componentsFixes available
Mozilla Thunderbird<159
159
Mozilla Thunderbird<153.6
153.6

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 159
  2. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 153.6
  3. Upgrade

    Upgrade Thunderbird to a version that resolves this vulnerability.

    Fixed in 159

Event History

Oct 27, 2026
CVE Published
via Mozilla·12:00 AM
Data Sourced
via Mozilla·12:00 AM
DescriptionSeverityAffected Software
CVE Published
via MITRE·06:16 PM
Data Sourced
via MITRE·06:16 PM
Description

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

Frequently Asked Questions

1

Which systems are affected?

Only Thunderbird running on Windows is affected. Other operating systems are unaffected.

2

What must an attacker do to exploit this issue?

An attacker must cause Thunderbird to display a specially crafted email containing a mailbox: URL that uses an extended-length UNC path. The crafted URL can make Thunderbird connect to an SMB server selected by the attacker.

3

What information could be exposed?

The SMB connection can disclose the user's Windows account name and NTLM authentication data. That data could be used for offline password cracking or relay attacks.

4

How can I determine whether I need to remediate?

Windows systems running Thunderbird versions before 159 need remediation. The issue was fixed in Thunderbird 159.

Company

Resources

Contact

SecAlerts Pty Ltd.
132 Wickham Terrace
Fortitude Valley,
QLD 4006, Australia
info@secalerts.co
By using SecAlerts services, you agree to our services end-user license agreement. This website is safeguarded by reCAPTCHA and governed by the Google Privacy Policy and Terms of Service. All names, logos, and brands of products are owned by their respective owners, and any usage of these names, logos, and brands for identification purposes only does not imply endorsement. If you possess any content that requires removal, please get in touch with us.
© 2026 SecAlerts Pty Ltd.
ABN: 70 645 966 203, ACN: 645 966 203