Description
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.
The NTLM credential leak only affects Thunderbird on Windows. Other operating systems are unaffected. This vulnerability was fixed in Thunderbird 159 and Thunderbird 153.6.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mozilla | Thunderbird | — | 153.6 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | thunderbird | No fix yet | — |
| Debian 13 | thunderbird | 1:153.6.0esr-1~deb13u1 | — |
| Debian 12 | thunderbird | 1:153.6.0esr-1~deb12u2 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 24.04 LTS | mozjs102 +1 | No fix yet | — |
| Ubuntu 22.04 LTS | mozjs78 +3 | No fix yet | — |
| Ubuntu 20.04 LTS | mozjs52 +1 | No fix yet | — |
| Ubuntu 18.04 LTS | mozjs38 +1 | No fix yet | — |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | MozillaThunderbird | 153.6.0-1.1 | openSUSE-SU-2026:12339-1 |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 10 | thunderbird | 153.6.0-1.0.1.el10_2 | ELSA-2026-96079 |
| Oracle Linux 9 | thunderbird | 153.6.0-1.0.1.el9_8 | ELSA-2026-96081 |
Advisories 4
- WID-SEC-2026-4216 Mozilla Firefox, Firefox ESR, und Thunderbird: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 12, 2026
- ELSA-2026-96079 Important: thunderbird security update (Oracle Linux 10) Oracle Linux Security Advisories (ELSA) · Nov 9, 2026
- ELSA-2026-96081 Important: thunderbird security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Nov 9, 2026
- openSUSE-SU-2026:12339-1 MozillaThunderbird-153.6.0-1.1 on GA media SUSE / openSUSE Security Updates · Oct 31, 2026