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CVE-2026-6657

8.8 · HIGH

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.

Published Jun 3, 2026CWE-346EPSS 0.27%

Overview

CVE-2026-6657 is a high-severity vulnerability. It was published on June 3, 2026 and has a CVSS 3.1 base score of 8.8 (HIGH).

This vulnerability has a CVSS 3.1 base score of 8.8, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refhuntr.com/bounties/18f642db-3569-43b3-b58d-ff97be4b09d7Refhuntr.com/bounties/18f642db-3569-43b3-b58d-ff97be4b09d7

How CyberStrike helps

Frequently asked questions

What is CVE-2026-6657?

CVE-2026-6657 is a high-severity vulnerability. It was published on June 3, 2026 and has a CVSS 3.1 base score of 8.8 (HIGH).

How severe is CVE-2026-6657?

This vulnerability has a CVSS 3.1 base score of 8.8, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-6657?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-6657?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-6657 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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