Quick answers
- Is CVE-2026-126133 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-126133 being exploited in the wild.
- How severe is CVE-2026-126133?
- Informational severity, published 10 November 2026.
- Which products and versions are affected?
- Mozilla Thunderbird before 160.
- Is there a fix for CVE-2026-126133?
- Yes: fixed in Thunderbird 160. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-126133 attacked?
- It is attacked over the network or from the adjacent network, in an operating system.
- Am I affected by CVE-2026-126133?
- Check whether you run Mozilla Thunderbird at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- Fixed in: Thunderbird 160
Technical details
When Thunderbird authenticates to an HTTP proxy to access CalDAV or ICS calendars, it incorrectly sends the calendar server's credentials (not proxy credentials) to the proxy. This occurs during both initial setup and periodic sync operations, and cached passwords are sent automatically without user interaction. An attacker with network position as the proxy can extract calendar credentials and use them to access the calendar directly.
Affected products
- Mozilla Thunderbird before 160
Timeline
- 2026-11-10: disclosed