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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-27145 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,238 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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
copyparty, a portable file server, has a DOM-based cross-site scripting vulnerability in versions prior to 1.16.15. The vulnerability is considered low-risk. 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 that, 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. Version 1.16.15 contains a fix.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | copyparty | all versions | 1.16.15pip install --upgrade 'copyparty==1.16.15' |
Detection & 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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-27145 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-27145. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-27145 in your dependencies?
O3 Security finds CVE-2025-27145 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.