Auth bypass in Nextcloud Calendar
CVE-2025-66546
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 class: IDOR (Insecure Direct Object Reference)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 3.3 (Low). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.
EPSS exploit prediction
EPSS: 0.001 (2.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 3rd percentile — 2.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: 0.000
Affected products
- Nextcloud Calendar — versions 6.0.0
- Nextcloud Security-Advisories — versions >= 6.0.0-rc.1, < 6.0.1, >= 5.0.0-rc.1, < 5.5.6, >= 3.0.0-beta1, < 4.7.19
Weakness classification (CWE)
References
- github.com/nextcloud/security-advisories/security/advisories/GHSA-7x2j-2674-fj95 (Patch, Vendor Advisory)
- github.com/nextcloud/calendar/pull/7537 (Issue Tracking)
- github.com/nextcloud/calendar/commit/f41650c3681fc4a4130eb883f5c0899c011326b3 (Patch)
- hackerone.com/reports/3275810 (Issue Tracking, Vendor Advisory)
Frequently asked questions
- What is CVE-2025-66546?
- CVE-2025-66546 is a low-severity vulnerability in Nextcloud Calendar, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 3.3/10. Published 2025-12-05.
- How severe is CVE-2025-66546?
- Low severity. CVSS v3 base score is 3.3 out of 10.