CVE-2026-6657Public exploitNetwork attack vector

CORS bypass via prefix-only origin matching

Published Jun 3, 2026 · Updated Jun 3, 2026

Origin validation error in Jupyter Server 1.12.0 through 2.17.0 allows remote attackers to bypass CORS restrictions via crafted domains. The allow_origin_pat checks use re.match() against Origin values, so a domain with an allowed prefix passes without matching the complete origin. Exploitation requires that configuration and user interaction with attacker-controlled content, enabling unauthorized API reads and writes in the victim's session.

CVSS severity8.8
High
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Origin validation error in Jupyter Server 1.12.0 through 2.17.0 allows remote attackers to bypass CORS restrictions via crafted domains. The allow_origin_pat checks use re.match() against Origin values, so a domain with an allowed prefix passes without matching the complete origin. Exploitation requires that configuration and user interaction with attacker-controlled content, enabling unauthorized API reads and writes in the victim's session.

The record

CVE
CVE-2026-6657
Published
Jun 3, 2026
Updated
Jun 3, 2026
Vendor
Project Jupyter
Product
Jupyter Server
Classifications
CWE-777, CWE-346, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <=latest

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Project Jupyter · Jupyter Serverversion=unspecified <=latest

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
5.9Project JupyterCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
6.1huntr.devCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-777Regular Expression without Anchors
CWE-346Origin Validation Error
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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