Nextcloud Calendar Blind Booking ID before v4.7.19,5.5.6,6.0.1 (CVE202566546)
CVE-2025-66546 Published on December 5, 2025
Nextcloud Calendar app allowed booking appointments without the generated token
Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.19, 5.5.6, and 6.0.1, the calendar app allowed blindly booking appointments with a squential ID without known the appointment token. This vulnerability is fixed in 4.7.19, 5.5.6, and 6.0.1.
Vulnerability Analysis
CVE-2025-66546 is exploitable with local system access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality, a small impact on integrity and availability.
Weakness Type
What is an Insecure Direct Object Reference / IDOR Vulnerability?
The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.
CVE-2025-66546 has been classified to as an Insecure Direct Object Reference / IDOR vulnerability or weakness.
Affected Versions
nextcloud security-advisories:- Version >= 6.0.0-rc.1, < 6.0.1 is affected.
- Version >= 5.0.0-rc.1, < 5.5.6 is affected.
- Version >= 3.0.0-beta1, < 4.7.19 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.