# CVE-2026-113866: thunderbird: When setting up an account, Thunderbird's Exchange AutoDiscover lookup also queried the domain's AutoDiscover service...

CVE-2026-113866 is fixed in thunderbird on 1 platform, first by DEBIAN-CVE-2026-113866, released October 27, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-113866
- Priority: Routine
- CVSS: 5.9 (medium)
- EPSS: 0.0037
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 20, 2026

## Description

When setting up an account, Thunderbird's Exchange AutoDiscover lookup also queried the domain's AutoDiscover service over plain HTTP. Due to a bug, that unencrypted request included the credentials the user had entered, allowing a network attacker to obtain the user's password. This vulnerability was fixed in Thunderbird 158.0.1 and Thunderbird 153.5.1.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | thunderbird Debian 12.15 (bookworm) | 1:153.5.1esr-1~deb12u1 | [DEBIAN-CVE-2026-113866](https://patchblox.com/security/data/fix/linux/debian-cve-2026-113866.md) | Oct 27, 2026 |
| Linux | thunderbird Debian 13.5 (trixie) | 1:153.5.1esr-1~deb13u1 | [DEBIAN-CVE-2026-113866](https://patchblox.com/security/data/fix/linux/debian-cve-2026-113866.md) | Oct 27, 2026 |

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Data as of 2026-11-10T07:50:38Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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