CVE-2026-66005Public exploitNetwork attack vector

Unauthenticated API access via wildcard host substitution

Published Jul 24, 2026 · Updated Jul 24, 2026

CORS policy bypass in Jan 0.8.4 and earlier allows remote attackers to access its local API through arbitrary Host and Origin values. When the server binds to 0.0.0.0, start_server_internal replaces configured trusted hosts with a wildcard, causing is_valid_host to accept every Host and reflect every Origin with credentials. Exposure requires a nondefault network bind; LAN access or DNS rebinding then enables model enumeration and inference, cross-origin response reads, and MCP tool invocation when server tool execution is enabled.

CVSS severity6.3
Medium
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

CORS policy bypass in Jan 0.8.4 and earlier allows remote attackers to access its local API through arbitrary Host and Origin values. When the server binds to 0.0.0.0, start_server_internal replaces configured trusted hosts with a wildcard, causing is_valid_host to accept every Host and reflect every Origin with credentials. Exposure requires a nondefault network bind; LAN access or DNS rebinding then enables model enumeration and inference, cross-origin response reads, and MCP tool invocation when server tool execution is enabled.

The record

CVE
CVE-2026-66005
Published
Jul 24, 2026
Updated
Jul 24, 2026
Vendor
Menlo Research Pte. Ltd.
Product
Jan
Classifications
CWE-183, CWE-942, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 24, 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=0 <=0.8.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Menlo Research Pte. Ltd. · Janversion=0 <=0.8.4

Published CVSS scores

5.3VulnCheck CNACVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N
6.3VulnCheck CNACVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-183Permissive List of Allowed Inputs
CWE-942Permissive Cross-domain Security Policy with Untrusted Domains
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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