CVE-2025-66514: Nextcloud Mail

Medium severity, CVSS 5.4. EPSS: 0.3% chance of exploitation in the next 30 days.

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.

Affected products

• Nextcloud Mail: before 5.5.3 (fixed in 5.5.3)

Published 2025-12-05. Last modified 2026-06-17.