Vulnerability in Nextcloud Calendar
CVE-2025-66550
Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.17 and 5.2.4, when a malicious user creates a calendar event with a crafted attachment that links to a download link of a file on the same Nextcloud server, the file would be downloaded without the user confirming the action. This vulnerability is fixed in 4.7.17 and 5.2.4.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.7 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.003 (26.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 26th percentile — 26.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000
Affected products
- Nextcloud Calendar
- Nextcloud Security-Advisories — versions >= 5.0.0-rc.1, < 5.2.4, < 4.7.17
Weakness classification (CWE)
References
- github.com/nextcloud/security-advisories/security/advisories/GHSA-f29c-ppmv-8mcv (Patch, Vendor Advisory)
- github.com/nextcloud/calendar/pull/6971 (Issue Tracking)
- github.com/nextcloud/calendar/commit/63a6c398db01391eb9fd5297a0d4c3d6e614f769 (Patch)
- hackerone.com/reports/3112033 (Issue Tracking, Vendor Advisory)
Frequently asked questions
- What is CVE-2025-66550?
- CVE-2025-66550 is a medium-severity vulnerability in Nextcloud Calendar, classified under CWE-241. CVSS score: 5.7/10. Published 2025-12-05.
- How severe is CVE-2025-66550?
- Medium severity. CVSS v3 base score is 5.7 out of 10.