Nextcloud Server <31.0.12/32.0.3 CSP Bypass via Unsanitized SVG
CVE-2025-66512 Published on December 5, 2025
Nextcloud Server vulnerable to XSS in SVG images when opened outside of Nextcloud
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.
Vulnerability Analysis
CVE-2025-66512 is exploitable with network access, requires user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, with no impact on integrity and availability.
Weakness Type
What is a Basic XSS Vulnerability?
The software receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages. This may allow such characters to be treated as control characters, which are executed client-side in the context of the user's session. Although this can be classified as an injection problem, the more pertinent issue is the improper conversion of such special characters to respective context-appropriate entities before displaying them to the user.
CVE-2025-66512 has been classified to as a Basic XSS vulnerability or weakness.
Products Associated with CVE-2025-66512
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Affected Versions
nextcloud security-advisories:- Version >= 32.0.0beta1, < 32.0.3 is affected.
- Version < 31.0.12 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.