CVE-2026-27948: Copyparty Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-62cr-6wp5-q43h
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CVSS 5.4
CWE-79
Published
Advisory Summary

CVE-2026-27948 is a MODERATE (CVSS 5.4) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Copyparty libraries in the PyPI ecosystem. The issue involves copyparty vulnerable to reflected xss via setck parameter. Remediation is available by upgrading affected packages to version 1.20.9.

CVE-2026-27948 at a Glance

CVE Identifier CVE-2026-27948
GHSA Identifier GHSA-62cr-6wp5-q43h
Severity MODERATE
CVSS v3.1 Base Score 5.4
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Copyparty
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 5.4

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Unchanged (S:U)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-27948

To remediate this vulnerability, upgrade all affected Copyparty dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

copyparty fixed: 1.20.9 
pip install copyparty>=1.20.9
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show copyparty

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-27948, inspect your installed packages using pip:

pip show copyparty

Analyze the terminal output to locate any version of Copyparty in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.20.9), your application is affected.

Note: The pip show copyparty command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Copyparty, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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).

CVE-2026-27948 Affected Copyparty Versions

1 component(s)
Fixed Versions:
1.20.9
Product / Package Ecosystem Affected Versions Fixed Version
copyparty
pypi/copyparty
PyPI
< 1.20.9
1.20.9

References

GitHub Advisory / Wiki ADVISORY
https://github.com/9001/copyparty/security/advisories/GHSA-62cr-6wp5-q43h
NVD — CVE-2026-27948 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27948
Security Fix Commit FIX COMMIT
https://github.com/9001/copyparty/commit/31b2801fd041f803f4a3d5c12c7d7cb5419048bc
Copyparty Source Repository REPOSITORY
https://github.com/9001/copyparty
Copyparty Release RELEASE
https://github.com/9001/copyparty/releases/tag/v1.20.9

Frequently Asked Questions

What is CVE-2026-27948?
CVE-2026-27948 is a security vulnerability in Copyparty involving Copyparty vulnerable to reflected XSS via setck parameter under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Copyparty versions are affected?
Affected versions include releases prior to 1.20.9 across affected packages: copyparty.
What version fixes CVE-2026-27948?
Upgrading to 1.20.9 (or the latest patched release for your respective branch) resolves the vulnerability.
Is copyparty affected?
Yes, copyparty is affected in releases prior to 1.20.9. Upgrade your dependency to 1.20.9 or later.
What is the CVSS score of CVE-2026-27948?
CVE-2026-27948 has a CVSS v3.1 base score of 5.4 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N.
What CWE is associated with CVE-2026-27948?
CVE-2026-27948 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check PyPI dependencies for CVE-2026-27948?
Run the dependency tree command: 'pip show copyparty'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-62cr-6wp5-q43h",
  "modified" : "2026-02-26T22:33:46Z",
  "published" : "2026-02-26T22:33:46Z",
  "aliases" : [ "CVE-2026-27948" ],
  "summary" : "Copyparty vulnerable to reflected XSS via setck parameter",
  "details" : "### Summary\nAn XSS allows for reflected cross-site scripting via URL-parameter `?setck=...`\n\n### Details\nA reflected cross-site scripting (XSS) vulnerability could allow an attacker to execute malicious javascript by tricking users into accessing a malicious link.\n\nThe 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.\n\n### Indicators of Compromise\nAll 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).",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "copyparty"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.20.9"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/9001/copyparty/security/advisories/GHSA-62cr-6wp5-q43h"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27948"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/9001/copyparty/commit/31b2801fd041f803f4a3d5c12c7d7cb5419048bc"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/9001/copyparty"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/9001/copyparty/releases/tag/v1.20.9"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-26T22:33:46Z",
    "nvd_published_at" : "2026-02-26T02:16:22Z"
  }
}