CVE-2025-27145 is a low-severity (CVSS 3.6) Cross-site Scripting (XSS) vulnerability in copyparty. A fix is available for copyparty — see the affected versions and patch details below.
copyparty renders unsanitized filenames as HTML when user uploads empty files
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-2025-27145.
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
A DOM-Based XSS was discovered in copyparty, a portable fileserver. The vulnerability is considered low-risk.
Details
By handing someone a maliciously-named file, and then tricking them into dragging the file into copyparty's Web-UI, an attacker could execute arbitrary javascript with the same privileges as that user. For example, this could give unintended read-access to files owned by that user. The bug is triggered by the drag-drop action itself; it is not necessary to actually initiate the upload. The file must be empty (zero bytes).
Note: As a general-purpose webserver, it is intentionally possible to upload HTML-files with arbitrary javascript in <script> tags, which will execute when the file is opened. The difference is that this vulnerability would trigger execution of javascript during the act of uploading, and not when the uploaded file was opened.
Proof of Concept (POC)
- Create an empty file named
<img src=x onerror="alert(1)"> - Drag-and-drop the file into the browser to initiate an upload
- The
alert(1)is executed
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | copyparty | all versions | 1.16.15pip install --upgrade 'copyparty==1.16.15' |
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 1.16.15 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-27145 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-2025-27145 in your dependencies?
Find it across PyPI, including transitive dependencies.