CVE-2025-66512Network attack vector

Stored XSS via unsanitized uploaded SVG markup

Published Dec 5, 2025 · Updated Dec 5, 2025

Stored XSS in Nextcloud Server and Server Enterprise before 31.0.12 or 32.0.3 allows attackers to run script via uploaded SVG files. The Viewer Images component loaded uploaded SVG markup without sanitization; the patch fetches the content, applies DOMPurify, and embeds the sanitized result as a data URL. Exploitation requires a victim to open an attacker-supplied SVG outside the Nextcloud web page, bypassing its content security policy and enabling script-controlled page changes or interruption.

CVSS severity5.4
Medium
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Stored XSS in Nextcloud Server and Server Enterprise before 31.0.12 or 32.0.3 allows attackers to run script via uploaded SVG files. The Viewer Images component loaded uploaded SVG markup without sanitization; the patch fetches the content, applies DOMPurify, and embeds the sanitized result as a data URL. Exploitation requires a victim to open an attacker-supplied SVG outside the Nextcloud web page, bypassing its content security policy and enabling script-controlled page changes or interruption.

The record

CVE
CVE-2025-66512
Published
Dec 5, 2025
Updated
Dec 5, 2025
Vendor
Nextcloud GmbH
Product
Security Advisories
Classifications
CWE-80, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 5, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 5, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 31.0.12
  2. Affected versionversion=>= 32.0.0beta1, < 32.0.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Nextcloud GmbH · Security Advisoriesversion=< 31.0.12; version=>= 32.0.0beta1, < 32.0.3

Published CVSS scores

5.4GitHub CNACVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-80Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
T1204.002Malicious File

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo