REDHAT-BUG-2567087: High severity Mozilla Thunderbird vulnerability

Q: Who is exposed to NTLM credential leakage?

Only Thunderbird users on Windows are exposed to NTLM credential leakage, because the malicious feed can cause a connection to an attacker-controlled network share. Users on other operating systems are affected by local file reads but not the described NTLM leak.

Q: What must an attacker control to exploit this issue?

An attacker must provide a malicious RSS feed or be able to modify a feed delivered over HTTP. The feed uses the itunes:new-feed-url or newLocation element to change the stored subscription URL to a file: URL.

Q: Does exploitation require repeated user interaction?

After the subscription URL has been changed, Thunderbird reads the file: location on every feed update. This makes the impact persistent for the affected stored subscription.

Q: Which Thunderbird releases contain the fix?

The issue was fixed in Thunderbird 159 and Thunderbird 153.6.

Published Nov 4, 2026

Updated

A remote RSS feed could use the itunes:new-feed-url or newLocation element to permanently change its stored subscription URL to a file: URL. Thunderbird then read that location on every feed update. This allowed a malicious feed, or an attacker able to modify a feed delivered over HTTP, to make Thunderbird read local files and, on Windows, connect to an attacker-controlled network share, which could leak the user's NTLM credentials. The NTLM credential leak only affects Thunderbird on Windows. Other operating systems are affected by the local file read only. This vulnerability was fixed in Thunderbird 159 and Thunderbird 153.6.

Affected Software

1 affected component

Mozilla Thunderbird<159, <153.6

Remediation

Recommended actions to resolve this vulnerability, in priority order.

Upgrade
Upgrade Thunderbird to a version that resolves this vulnerability.
Fixed in 159

Event History

Nov 4, 2026

Data Sourced

via Red Hat·04:28 PM

DescriptionSeverityAffected Software

Frequently Asked Questions

Who is exposed to NTLM credential leakage?

Only Thunderbird users on Windows are exposed to NTLM credential leakage, because the malicious feed can cause a connection to an attacker-controlled network share. Users on other operating systems are affected by local file reads but not the described NTLM leak.

What must an attacker control to exploit this issue?

An attacker must provide a malicious RSS feed or be able to modify a feed delivered over HTTP. The feed uses the itunes:new-feed-url or newLocation element to change the stored subscription URL to a file: URL.

Does exploitation require repeated user interaction?

After the subscription URL has been changed, Thunderbird reads the file: location on every feed update. This makes the impact persistent for the affected stored subscription.

Which Thunderbird releases contain the fix?

The issue was fixed in Thunderbird 159 and Thunderbird 153.6.

REDHAT-BUG-2567087: High severity Mozilla Thunderbird vulnerability

Affected Software

Remediation

Event History

Frequently Asked Questions

Who is exposed to NTLM credential leakage?

What must an attacker control to exploit this issue?

Does exploitation require repeated user interaction?

Which Thunderbird releases contain the fix?

Company

Resources

Contact

Frequently Asked Questions

Who is exposed to NTLM credential leakage?

What must an attacker control to exploit this issue?

Does exploitation require repeated user interaction?

Which Thunderbird releases contain the fix?