CVE-2025-66514

Nextcloud Mail stored HTML injection in subject text

3.5 Low

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.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: Low
User interaction: Required

What an attacker can affect

Confidentiality: None
Integrity: Low
Availability: None

Exploit likelihood

0.27%Up 0.2 points since Dec 6, 2025

What each source reports

CVE List Score used 3.5

Nextcloud Mail stored HTML injection in subject text

Record: CVE-2025-66514
CVSS 3.1: 3.5 LowCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N
Weakness: CWE-79
Updated: 2026-11-02

EUVDEUVD-2025-201464 3.5

Record: EUVD-2025-201464
CVSS 3.1: 3.5 LowCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N
Updated: 2026-11-02

NVD 3.5

Record: CVE-2025-66514
CVSS 3.1: 3.5 LowCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N
CVSS 3.1: 5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Weakness: CWE-79
Updated: 2026-11-02

OSV 3.5

Nextcloud Mail stored HTML injection in subject text

Record: CVE-2025-66514
CVSS 3.1: 3.5 LowCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N
Weakness: CWE-79
Updated: 2026-11-02

Affected products

History

History
Recorded	Changed	Sources
Nov 2, 2026	first indexed	CVE List, EUVD, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2025-66514 is a low vulnerability (CVSS 3.5) in Nextcloud Mail, published December 5, 2025. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.27%, the 19th percentile. No source names a fixed version.