---
id: "CVE-2026-126133"
page: "https://infrastack.ai/live/CVE-2026-126133"
kind: "vulnerability"
aliases: ["CVE-2026-126133"]
title: "Thunderbird: calendar passwords sent to a malicious HTTP proxy"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["caldav", "ics", "package", "thunderbird"]
not_affected_if: ["no-authenticating-proxy", "no-calendar-sync"]
published_at: "2026-11-10T19:21:13+00:00"
first_seen_at: "2026-11-10T19:25:15+00:00"
updated_at: "2026-11-10T20:04:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-126133", "first_seen_at": "2026-11-10T19:25:15+00:00"}]
exploit_sources: []
---

# Thunderbird: calendar passwords sent to a malicious HTTP proxy

Link for people: https://infrastack.ai/live/CVE-2026-126133 (this .md is for agents)

When Thunderbird reaches a CalDAV or ICS calendar through an HTTP proxy that asks for authentication, it can reply to the proxy with the calendar server's saved username and password. A malicious or compromised proxy can collect those calendar credentials, including for HTTPS calendars.

_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; versions below `160` are affected.
- Check whether calendars (CalDAV or ICS) are configured and whether the connection goes through an HTTP proxy that requires authentication.

## Fix

- Thunderbird `160`

## Timeline

- 2026-11-10T19:25:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-126133

## From the sources

When a CalDAV or ICS calendar was accessed through an HTTP proxy that requested authentication, Thunderbird could answer the proxy with the calendar server's username and password. This affected both setting up a new calendar and syncing existing calendars, where a saved password could be sent without any user interaction. A malicious or compromised proxy could use this to obtain the calendar credentials, even for calendars served over HTTPS. This vulnerability was fixed in Thunderbird 160.

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_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_