CVE-2026-6657: jupyter jupyter_server Origin Validation Error

Vulnerability summary

CVE-2026-6657 is a high (CVSS 8.8) Origin Validation Error vulnerability in jupyter jupyter_server. EPSS estimates a 0.27% chance of exploitation in the next 30 days, higher than 18.2% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 03-06-2026
   PublishedVulnerability first disclosed.
2. 03-06-2026
   Last modifiedVulnerability information updated.

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.

• CWE-346Origin Validation ErrorThe product does not properly verify that the source of data or communication is valid.