CVE-2026-6657
Description
A flaw was found in jupyter-server. A remote attacker can bypass Cross-Origin Resource Sharing (CORS) origin validation when the allow_origin_pat configuration is used. This vulnerability allows malicious domains to pass validation against patterns intended for trusted domains. This could lead to arbitrary code execution, unauthorized access to sensitive API responses, and phishing attacks.
Statement
The impact for this flaw is set to Moderate because exploitation requires (1) allow_origin_pat to be configured — a non-default CORS regex allowlist; when allow_origin is set it takes precedence (2) user interaction: the victim must visit an attacker-controlled origin while authenticated to Jupyter. In that case, broken re.match() validation can allow cross-origin Jupyter API access (CWE-346). This is not unauthenticated RCE on default supported configurations.
Mitigation
Restrict network access to the jupyter-server to only trusted clients and networks. This can be achieved by configuring firewall rules to limit inbound connections to the ports used by jupyter-server, thereby reducing the attack surface for this CORS bypass vulnerability. A restart or service reload may be required for firewall changes to take effect.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.1 | 8.8 | 6.1 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | Low | Low | Low |
| Privileges Required | None | None | None |
| User Interaction | Required | Required | Required |
| Scope | Changed | Unchanged | Changed |
| Confidentiality | Low | High | Low |
| Integrity Impact | Low | High | Low |
| Availability Impact | None | High | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
cve.org: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
