CVE-2026-118180: Matrix homeserver could redirect the chat session to a local file or network share

Published Oct 27, 2026
·
Updated

When logging in to a Matrix account, Thunderbird used the homeserver address provided in the server's login response without validating it. A malicious or compromised homeserver could provide a file: URL, causing Thunderbird to send all further Matrix requests of that session to local files or, on Windows, to an attacker-controlled network share, which could leak the user's NTLM credentials.

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

Who can exploit this issue?

A malicious or compromised Matrix homeserver can exploit it during login by supplying an unvalidated homeserver address in its login response.

2

Which systems face the NTLM credential leak risk?

The NTLM credential leak affects Thunderbird on Windows only. Other operating systems are not affected by that credential-leak scenario.

3

What happens if exploitation succeeds?

Thunderbird can send subsequent Matrix requests in that session to local files or, on Windows, to an attacker-controlled network share. Access to the network share may leak the user's NTLM credentials.

4

What should organizations do?

Update to Thunderbird 159, which fixes the vulnerability.

Company

Resources

Contact

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