---
id: "CVE-2026-113866"
kind: "vulnerability"
aliases: ["CVE-2026-113866"]
title: "Thunderbird: account setup leaks user password over plain HTTP"
severity: "medium"
cvss: 5.9
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["desktop-email", "exchange", "package", "thunderbird"]
not_affected_if: ["already-on-fixed-version", "no-exchange-account-setup"]
published_at: "2026-10-20T20:17:19+00:00"
first_seen_at: "2026-10-23T21:57:21+00:00"
updated_at: "2026-10-25T04:08:39+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-113866", "first_seen_at": "2026-10-23T21:57:21+00:00"}]
---

# Thunderbird: account setup leaks user password over plain HTTP

When Thunderbird sets up an account, its Exchange AutoDiscover lookup also sends a request to the domain's AutoDiscover service over unencrypted HTTP. That request carried the password the user typed, so a network attacker can read it.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `thunderbird --version` (or check Help > About Thunderbird) and compare against the fixed versions.
- unknown

## Fix

- Update Thunderbird to `158.0.1` or `153.5.1`, whichever matches your release line.

## Timeline

- 2026-10-23T21:57:21+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-113866

## From the sources

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.

---

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