Description
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.
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