Public proof of concept

CVE-2026-6657

A public proof of concept exists; no exploitation attested.

Published2026-06-03
WeaknessCWE-346

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC

2026-06-0316:16CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-25 15:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-6657?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-6657?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

OSV · NVD

jupyter-server

Branch	Affected	Fixed in	Source
2.17	≥ 1.12.0, ≤ 2.17.0	no fix published	OSV

Jupyter jupyter server

Branch	Affected	Fixed in	Source
2.17	≥ 1.12.0, ≤ 2.17.0	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

No fix published by the sources we read yet. NVD record

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CISA-ADPSSVC decisionpoc2026-06-03
OpenCVESSVC decisionpoc—
NVDCVSS 3.18.8read 2026-10-23
CNACVSS 3.06.1read 2026-10-23
CNAweakness (CWE)CWE-346read 2026-10-23
FIRST EPSSEPSS score6.2 %2026-10-25
OSVaffected packages—

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Published: 2026-06-03
Last Modified: 2026-07-21
NVD status: Analyzed

Frequently asked questions

What is CVE-2026-6657?

Is CVE-2026-6657 actively exploited?

A proof-of-concept exploit exists for CVE-2026-6657, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-6657?

CVE-2026-6657 has a CVSS v3 base score of 8.8 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

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