copyparty renders unsanitized filenames as HTML when user uploads empty files

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

3.6 · CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N

EPSS

• CVE-2025-27145: 0.47% estimated exploitation activity in the next 30 days; percentile 40.62 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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) 1. Create an empty file named <img src=x onerror="alert(1)" 2. Drag-and-drop the file into the…

Published by the source

26 Feb 2025, 20:06 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:31 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m2jw-cj8v-937r

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-m2jw-cj8v-937r

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# Patch Next advisory brief: CVE-2025-27145

Advisory: copyparty renders unsanitized filenames as HTML when user uploads empty files
IDs: CVE-2025-27145, GHSA-m2jw-cj8v-937r
Record: https://patchnext.com/advisories/cve-2025-27145 (revision 2, source checked 26 Oct 2026, 13:31 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: copyparty 1.16.15. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI copyparty: affected < 1.16.15; fixed in 1.16.15

## Suggested inspection (read-only)
- `python -m pip show copyparty`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on copyparty.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-m2jw-cj8v-937r (OSV record GHSA-m2jw-cj8v-937r lists affected ranges: PyPI copyparty >=0 <1.16.15 (fixed))
- Verified: https://github.com/advisories/GHSA-m2jw-cj8v-937r (GitHub-reviewed advisory GHSA-m2jw-cj8v-937r lists affected ranges: PyPI copyparty >=0 <1.16.15)

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