---
id: "CVE-2026-118177"
kind: "vulnerability"
aliases: ["CVE-2026-118177"]
title: "Thunderbird: calendar discovery accepts remote and local locations, leaking NTLM"
severity: "medium"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["calendar", "package", "thunderbird", "windows"]
not_affected_if: ["fixed-version", "no-calendar-discovery"]
published_at: "2026-10-27T19:17:29+00:00"
first_seen_at: "2026-10-27T19:33:18+00:00"
updated_at: "2026-10-27T19:35:09+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-118177", "first_seen_at": "2026-10-27T19:33:18+00:00"}]
---

# Thunderbird: calendar discovery accepts remote and local locations, leaking NTLM

When Thunderbird looks up calendars in a server directory during account setup or when adding a network calendar, it accepts locations pointing to other servers, local files or network shares. A malicious server or a network attacker on plain HTTP can make Thunderbird subscribe to such a location, leaking NTLM credentials on Windows and letting calendar changes overwrite files on the attacker's share or a local file.

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

## How to check

- Check the installed Thunderbird version under Help > About Thunderbird, or run `thunderbird --version` on the command line
- Check whether Thunderbird is used on Windows with calendars discovered from a server or added as network calendars

## Fix

- Update Thunderbird to `159` or `153.6` or later

## Timeline

- 2026-10-27T19:33:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-118177

## From the sources

When looking for calendars in a directory on a server, during account setup or when adding a new network calendar, Thunderbird accepted calendar locations pointing to other servers, local files or network shares. A malicious server, or a network attacker when the lookup used plain HTTP, could make Thunderbird subscribe to such a location. On Windows this could leak the user's NTLM credentials to an attacker-controlled host on every calendar refresh, and changes to the calendar could be written to the attacker's share or overwrite a local file. This vulnerability was fixed in Thunderbird 159 and Thunderbird 153.6.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_