CVE-2026-6657
Published: 03 June 2026
Summary
CVE-2026-6657 is a high-severity Origin Validation Error (CWE-346) vulnerability in Jupyter Jupyter Server. Its CVSS base score is 8.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 9.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-34104
Vulnerability details
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…
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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(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CORS origin validation bypass in publicly exposed Jupyter server directly enables exploitation of the application for unauthorized access and code execution.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Requires unique identification of the service before communications, addressing failures to validate the origin of the interaction.
Trusted path establishment enforces validation that the communication originates from and reaches only the intended trusted system components.
Enforces validation of the true origin of DNS responses via signatures and chain-of-trust mechanisms.
Enforces origin validation of name/address data, eliminating reliance on unverified or impersonated DNS sources.
Mandates origin validation so that only legitimate endpoints can continue the authenticated session.