XSS in Nextcloud Mail
CVE-2025-66514
Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform. Prior to 5.5.3, a stored HTML injection in the Mail app's message list allowed an authenticated user to inject HTML into the email subjects. Javascript was correctly blocked by the content security policy of the Nextcloud Server code.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 3.5 (Low). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (14.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 15th percentile — 14.7% 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 Mail
- Nextcloud Security-Advisories — versions >= 5.2.0-beta.1, < 5.5.3
Weakness classification (CWE)
References
- github.com/nextcloud/security-advisories/security/advisories/GHSA-v394-8gpc-6fv5 (Patch, Vendor Advisory)
- github.com/nextcloud/mail/pull/11740 (Patch, Issue Tracking)
- github.com/nextcloud/mail/commit/c64fcc3b79e0c089b5e1d2e04a07bfa740b2ac09 (Patch)
- hackerone.com/reports/3357036 (Permissions Required, Vendor Advisory)
Frequently asked questions
- What is CVE-2025-66514?
- CVE-2025-66514 is a low-severity vulnerability in Nextcloud Mail, classified under Cross-site Scripting. CVSS score: 3.5/10. Published 2025-12-05.
- How severe is CVE-2025-66514?
- Low severity. CVSS v3 base score is 3.5 out of 10.