CVE-2026-6657: Duplicate Advisory Jupyter-server Is Vulnerable To CORS Vulnerability

MODERATE
Advisory Identifier: GHSA-v42x-x7jp-845h
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CVSS 6.1
CWE-346
Published
Advisory Summary

CVE-2026-6657 is a MODERATE (CVSS 6.1) jupyter-server is vulnerable to cors vulnerability (CWE-346: Origin Validation Error) affecting Duplicate Advisory libraries in the PyPI ecosystem. The issue involves jupyter-server is vulnerable to cors origin validation bypass when the `allow_origin_pat` configuration is used. Remediation is available in the latest vendor maintenance releases.

CVE-2026-6657 at a Glance

CVE Identifier CVE-2026-6657
GHSA Identifier GHSA-v42x-x7jp-845h
Severity MODERATE
CVSS v3.1 Base Score 6.1
CWE Classification CWE-346: Origin Validation Error
Affected Product Duplicate Advisory
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 6.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/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 Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-6657

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

jupyter-server fixed: Latest secure release 
pip install jupyter-server>=Latest secure release
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 jupyter-server

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-6657, inspect your installed packages using pip:

pip show jupyter-server

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

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

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-346: Origin Validation Error, where the product does not properly verify that the source of data or communication is valid. In Duplicate Advisory, 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

### Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-24qx-w28j-9m6p. This link is maintained to preserve external references. ### Original Description A vulnerability in jupyter-server versions 1.12.0 through 2.17.0 allows an attacker to bypass CORS origin validation when the `allow_origin_pat` configuration is used. The issue arises from the use of `re.match()` for validating the `Origin` header, which only anchors at the start of the string. This allows attacker-controlled domains such as `trusted.example.com.evil.com` to pass validation against patterns intended to match `trusted.example.com`. The vulnerability affects multiple locations in the codebase, including CORS headers, WebSocket connections, referer validation, and login redirects, potentially enabling phishing attacks, arbitrary code execution, and unauthorized access to sensitive API responses.

CVE-2026-6657 Affected Duplicate Advisory Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
jupyter-server
pypi/jupyter-server
PyPI
≥ 1.12.0
≤ 2.17.0

References

NVD — CVE-2026-6657 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6657
GitHub Advisory / Wiki ADVISORY
https://github.com/advisories/GHSA-v42x-x7jp-845h
Duplicate Advisory Source Repository REPOSITORY
https://github.com/jupyter-server/jupyter_server
Duplicate Advisory Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/jupyter-server/PYSEC-2026-3472.yaml
huntr.com/bounties/18f642db-3... WEB
https://huntr.com/bounties/18f642db-3569-43b3-b58d-ff97be4b09d7
pypi.org/project/jupyter-ser... WEB
https://pypi.org/project/jupyter-server

Frequently Asked Questions

What is CVE-2026-6657?
CVE-2026-6657 is a security vulnerability in Duplicate Advisory involving jupyter-server is vulnerable to CORS origin validation bypass when the `allow_origin_pat` configuration is used under CWE-346: Origin Validation Error.
Which Duplicate Advisory versions are affected?
Affected versions include releases prior to current release patches across affected packages: jupyter-server.
What version fixes CVE-2026-6657?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is jupyter-server affected?
Yes, jupyter-server is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2026-6657?
CVE-2026-6657 has a CVSS v3.1 base score of 6.1 (MODERATE) with vector string CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2026-6657?
CVE-2026-6657 is classified under CWE-346: Origin Validation Error (The product does not properly verify that the source of data or communication is valid.).
How can I check PyPI dependencies for CVE-2026-6657?
Run the dependency tree command: 'pip show jupyter-server'. 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-v42x-x7jp-845h",
  "modified" : "2026-07-31T20:25:54Z",
  "published" : "2026-06-03T18:33:10Z",
  "withdrawn" : "2026-07-31T20:25:54Z",
  "aliases" : [ "CVE-2026-6657" ],
  "summary" : "Duplicate Advisory: jupyter-server is vulnerable to CORS origin validation bypass when the `allow_origin_pat` configuration is used",
  "details" : "### Duplicate Advisory\nThis advisory has been withdrawn because it is a duplicate of GHSA-24qx-w28j-9m6p. This link is maintained to preserve external references.\n\n### Original Description\nA vulnerability in jupyter-server versions 1.12.0 through 2.17.0 allows an attacker to bypass CORS origin validation when the `allow_origin_pat` configuration is used. The issue arises from the use of `re.match()` for validating the `Origin` header, which only anchors at the start of the string. This allows attacker-controlled domains such as `trusted.example.com.evil.com` to pass validation against patterns intended to match `trusted.example.com`. The vulnerability affects multiple locations in the codebase, including CORS headers, WebSocket connections, referer validation, and login redirects, potentially enabling phishing attacks, arbitrary code execution, and unauthorized access to sensitive API responses.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "jupyter-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.12.0"
      }, {
        "last_affected" : "2.17.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-6657"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-v42x-x7jp-845h"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jupyter-server/jupyter_server"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/jupyter-server/PYSEC-2026-3472.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://huntr.com/bounties/18f642db-3569-43b3-b58d-ff97be4b09d7"
  }, {
    "type" : "WEB",
    "url" : "https://pypi.org/project/jupyter-server"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-346" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-13T17:46:17Z",
    "nvd_published_at" : "2026-06-03T16:16:31Z"
  }
}