CVE-2026-27948 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 vulnerable to eflected cross-site scripting via setck parameter
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27948.
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-2026-27948 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 379,145 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
Summary
An XSS allows for reflected cross-site scripting via URL-parameter ?setck=...
Details
A reflected cross-site scripting (XSS) vulnerability could allow an attacker to execute malicious javascript by tricking users into accessing a malicious link.
The worst-case outcome of this is being able to move or delete existing files on the server, or upload new files, using the account of the person who clicks the malicious link.
Indicators of Compromise
All attempted attacks (successful or not) would be logged to both the copyparty serverlog and the accesslog of the reverseproxy, and are detected by grep -E '[?&]setck=[^&"]*%' (the text setck= eventually followed by the % character).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | copyparty | all versions | 1.20.9pip install --upgrade 'copyparty==1.20.9' |
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 1.20.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27948 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-2026-27948 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-27948. 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-2026-27948 in your dependencies?
O3 Security finds CVE-2026-27948 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.