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Vulnerability · Published Jun 3, 2026 · Assigned by @huntr_ai

CVE-2026-6657CORS Origin Validation Bypass in jupyter-server

Medium 6.1

In plain English

A medium-severity security flaw in jupyter/jupyter from jupyter. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 5.2% (higher than 93% of all known vulnerabilities).

Severity (CVSS 3.0)6.1Medium
Exploit odds (30 days)5.2%top 7.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12jupyter-serverno fix listedDEBIAN-CVE-2026-6657
Debian:13jupyter-serverno fix listedDEBIAN-CVE-2026-6657
Debian:14jupyter-serverno fix listedDEBIAN-CVE-2026-6657
PyPIjupyter-serverno fix listedGHSA-v42x-x7jp-845h
PyPIjupyter-serverno fix listedPYSEC-2026-3472
Ubuntu:22.04:LTSjupyter-serverno fix listedUBUNTU-CVE-2026-6657
Ubuntu:24.04:LTSjupyter-serverno fix listedUBUNTU-CVE-2026-6657
Ubuntu:25.10jupyter-serverno fix listedUBUNTU-CVE-2026-6657
Ubuntu:26.04:LTSjupyter-serverno fix listedUBUNTU-CVE-2026-6657
Ubuntu:26.10jupyter-serverno fix listedUBUNTU-CVE-2026-6657

Affected products (as reported)

VendorProductVersions
jupyter jupyter/jupyter unspecified – through latest

Weakness: CWE-346 · Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

References