XSS in Nextcloud Server
CVE-2025-66512
Nextcloud Server is a self hosted personal cloud system. In Nextcloud Server and Server Enterprise prior to 31.0.12 and 32.0.3, a missing sanitization allowed malicious users to circumvent the content security policy when a malicious user manages to trick a user it viewing an uploaded SVG outside of the Nextcloud Servers web page.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L.
EPSS exploit prediction
EPSS: 0.003 (18.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 18th percentile — 18.4% 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 >= 32.0.0beta1, < 32.0.3, < 31.0.12
Weakness classification (CWE)
References
- github.com/nextcloud/security-advisories/security/advisories/GHSA-qcw2-p26m-9gc5 (Patch, Vendor Advisory)
- github.com/nextcloud/viewer/pull/3023 (Issue Tracking)
- github.com/nextcloud/viewer/commit/5044a27d61bc40c0f134298d36af91f865335b63 (Patch)
- hackerone.com/reports/3357808 (Issue Tracking, Vendor Advisory)
Frequently asked questions
- What is CVE-2025-66512?
- CVE-2025-66512 is a medium-severity vulnerability in Nextcloud Server, classified under Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS). CVSS score: 5.4/10. Published 2025-12-05.
- How severe is CVE-2025-66512?
- Medium severity. CVSS v3 base score is 5.4 out of 10.