Auth bypass in Nextcloud Server
CVE-2025-66547
Nextcloud Server is a self hosted personal cloud system. In Nextcloud Server and Enterprise Server prior to 31.0.1, non-privileged users can modify tags on files they should not have access to via bulk tagging. This vulnerability is fixed in 31.0.1.
Vulnerability class: IDOR (Insecure Direct Object Reference)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (18.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 18th percentile — 18.3% 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 Server
- Nextcloud Security-Advisories — versions < 31.0.1
Weakness classification (CWE)
References
- github.com/nextcloud/security-advisories/security/advisories/GHSA-hq6c-r898-fgf2 (Patch, Vendor Advisory)
- github.com/nextcloud/server/issues/51247 (Issue Tracking)
- github.com/nextcloud/server/pull/51288 (Issue Tracking)
- github.com/nextcloud/server/commit/b44f1568f2dc97c746281d99e2342ad679e3d8a9 (Patch)
- hackerone.com/reports/3040887 (Permissions Required, Vendor Advisory)
Frequently asked questions
- What is CVE-2025-66547?
- CVE-2025-66547 is a medium-severity vulnerability in Nextcloud Server, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 4.3/10. Published 2025-12-05.
- How severe is CVE-2025-66547?
- Medium severity. CVSS v3 base score is 4.3 out of 10.