CVE-2026-126133 Calendar server credentials could be sent to an HTTP proxy
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-126133?
CVE-2026-126133 is a vulnerability in Mozilla Thunderbird, published on 10 Nov 2026.
Official description
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 and Thunderbird 153.7.
Which versions are affected by CVE-2026-126133?
How do I fix CVE-2026-126133?
Upgrade to a fixed version.
Is CVE-2026-126133 being exploited?
There is no known exploitation of CVE-2026-126133 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-126133, GHSA-c6f8-6299-g8jq, UBUNTU-CVE-2026-126133.