Vulnerability in Nextcloud Calendar
CVE-2025-66511
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.
EPSS: 0.003 (21.7th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 4.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N.
Affected products
- Nextcloud Calendar
- Nextcloud Security-advisories — versions >= 6.0.0-rc.1, < 6.0.3
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Patch, Vendor Advisory)
- security-advisories@github.com (x_refsource_MISC, Issue Tracking)
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (Permissions Required, x_refsource_MISC, Vendor Advisory)
Frequently asked questions
- What is CVE-2025-66511?
- CVE-2025-66511 is a medium-severity vulnerability in Nextcloud Calendar, classified under Use of Insufficiently Random Values. CVSS score: 4.8/10. Published 2025-12-05.
- How severe is CVE-2025-66511?
- Medium severity. CVSS v3 base score is 4.8 out of 10.