How to fix CVE-2025-66512?

Within 30 days: Identify affected systems running Nextcloud Server and Server Enterprise and apply vendor patches as part of regular patch cycle. Vendor patch is available.

Is Nextcloud Server affected by CVE-2025-66512?

Organizations using Nextcloud Server and Server Enterprise should be aware of moderate risk from CVE-2025-66512 rated CVSS 5.4. Exploitation could compromise the security of affected deployments. A patch is available and should be applied during regular vulnerability management.

CVE-2025-66512

EUVD-2025-201449 MEDIUM

2025-12-05 [email protected]

5.4

CVSS 3.1

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

Low

Lifecycle Timeline

Analysis Generated

Mar 15, 2026 - 17:08 vuln.today

EUVD ID Assigned

Mar 15, 2026 - 17:08 euvd

EUVD-2025-201449

Patch Released

Mar 15, 2026 - 17:08 nvd

Patch available

CVE Published

Dec 05, 2025 - 17:16 nvd

MEDIUM 5.4

Description

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.

Analysis

Technical Context

Cross-site scripting (XSS) allows injection of client-side scripts into web pages viewed by other users due to insufficient output encoding. This vulnerability is classified as Basic XSS (CWE-80).

Affected Products

Affected products: Nextcloud Nextcloud Server

Remediation

A vendor patch is available — apply it immediately. Encode all user-supplied output contextually (HTML, JS, URL). Implement Content Security Policy (CSP) headers. Use HTTPOnly and Secure cookie flags.

Priority Score

Low Medium High Critical

KEV: 0

EPSS: +0.0

CVSS: +27

POC: 0

Vendor Status

Debian

Bug #941708

nextcloud-server

Release	Status	Fixed Version	Urgency
	open	-	-

CVE-2025-66512 vulnerability details – vuln.today

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CVE-2025-66512

CVSS Vector

Lifecycle Timeline

Tags

Description

Analysis

Technical Context

Affected Products

Remediation

Priority Score

Vendor Status

Debian

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CVE-2025-66512

CVSS Vector

Lifecycle Timeline

Tags

Description

Analysis

Technical Context

Affected Products

Remediation

Priority Score

Vendor Status

Debian

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External POC / Exploit Code