CVE-2025-66511: Nextcloud Calendar is a calendar app for Nextcloud. Prior to 6.0.3, the Calendar app generates participant tokens for…
CVE-2025-66511 · Severity: medium · CVSS 4.8 · Published 2025-12-05
Nextcloud Calendar is a calendar app for Nextcloud. Prior to 6.0.3, the Calendar app generates participant tokens for meeting proposals using a hash function, allowing an attacker to compute valid participant tokens, which allowed them to request details and submit dates in meeting proposals. The tokens are not purely random generated. This vulnerability is fixed in 6.0.3.
No. Junglewise Threat Intelligence has no report of CVE-2025-66511 being exploited in the wild.
How severe is CVE-2025-66511?
Medium severity, with a CVSS score of 4.8, published 5 December 2025.
Which products and versions are affected?
Nextcloud Calendar. The advisory does not name versions.
Is there a fix for CVE-2025-66511?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
Am I affected by CVE-2025-66511?
Check whether you run Nextcloud Calendar. 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.