CVE-2026-30974: Copyparty volflag `nohtml` did not block javascript in svg files
Summary The nohtml config option, intended to prevent execution of JavaScript in user-uploaded HTML files, did not apply to SVG images.
Details A user with write-permission could upload an SVG containing embedded JavaScript, which would execute in the context of whichever user opens it.
This in itself is not a vulnerability; it is intended behavior according to the SVG spec. The vulnerability is that the nohtml volflag, when enabled, did not prevent this.
nohtml, intended for use on volumes which contains untrusted files, would correctly prevent execution of javascript in HTML files, but did not consider SVG images. This has been fixed in v1.20.11.
Impact The malicious JavaScript could move or delete existing files on the server, or upload new files, using the account of the person who opens the SVG.
Other sources
Copyparty is a portable file server. Prior to v1.20.11., the nohtml config option, intended to prevent execution of JavaScript in user-uploaded HTML files, did not apply to SVG images. A user with write-permission could upload an SVG containing embedded JavaScript, which would execute in the context of whichever user opens it. This has been fixed in v1.20.11.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-30974?
CVE-2026-30974 is considered a high severity vulnerability due to the potential for executing malicious JavaScript embedded in SVG files.
How do I fix CVE-2026-30974?
To fix CVE-2026-30974, upgrade to Copyparty version 1.20.11 or later.
What is the impact of CVE-2026-30974?
The impact of CVE-2026-30974 allows an attacker to execute JavaScript within the context of a user who opens a malicious SVG file.
Which software is affected by CVE-2026-30974?
CVE-2026-30974 affects Copyparty versions up to 1.20.10.
Who can exploit CVE-2026-30974?
A user with write permissions can exploit CVE-2026-30974 by uploading a specially crafted SVG file containing JavaScript.