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.

• CWE-79

• https://github.com/nextcloud/mail/commit/c64fcc3b79e0c089b5e1d2e04a07bfa740b2ac09Patch
• https://github.com/nextcloud/mail/pull/11740Issue Tracking, Patch
• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-v394-8gpc-6fv5Patch, Vendor Advisory
• https://hackerone.com/reports/3357036Permissions Required, Vendor Advisory

Published

Dec 5, 2025

Last Modified

Jun 17, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
• Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
• PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
• AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.

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