CVE-2026-66005
Received Received - Intake

CORS Misconfiguration in Jan Local API Server Allows Network Adjacent Attacks

Publication date: 2026-07-24

Last updated on: 2026-07-24

Assigner: VulnCheck

Description
Jan through 0.8.4, fixed in commit 3e1c1e7, contains a CORS misconfiguration vulnerability in its local API server that allows network-adjacent attackers to bypass trusted host restrictions by exploiting the server's replacement of user-configured trusted hosts with a wildcard that reflects arbitrary origins with credentials. Attackers on the local network or using DNS rebinding can reach the unauthenticated OpenAI-compatible API to perform inference, enumerate models, invoke MCP tools, and read cross-origin responses.

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Meta Information

Published
2026-07-24
Last Modified
2026-07-24
Generated
2026-07-24
AI Q&A
2026-07-24
EPSS Evaluated
N/A
NVD
CVE-2026-66005
EUVD
EUVD-2026-48611

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
janhq jan to 0.8.4 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-183 The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are explicitly allowed by policy because the inputs are assumed to be safe, but the list is too permissive - that is, it allows an input that is unsafe, leading to resultant weaknesses.
CWE-942 The product uses a web-client protection mechanism such as a Content Security Policy (CSP) or cross-domain policy file, but the policy includes untrusted domains with which the web client is allowed to communicate.

Attack-Flow Graph

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Executive Summary

CVE-2026-66005 is a CORS misconfiguration in the Jan application's local API server. When the server is bound to 0.0.0.0, it replaces the user-configured trusted hosts allowlist with a wildcard, disabling host-based restrictions. This allows network-adjacent attackers to bypass security controls and access the unauthenticated OpenAI-compatible API.

Detection Guidance

Check if Jan's local API server is bound to 0.0.0.0 instead of 127.0.0.1. Inspect network bindings using commands like 'netstat -tuln | grep 0.0.0.0' or 'ss -tuln | grep 0.0.0.0' on Linux. Verify if the Trusted Hosts allowlist is enforced by checking configuration files or logs for wildcard overrides.

Impact Analysis
  • Attackers on the local network or via DNS rebinding can access the API to perform inference, enumerate models, invoke MCP tools, and read cross-origin responses.
  • Unauthorized access to the API may lead to data exposure or manipulation if MCP tools are enabled.
  • The default binding to 127.0.0.1 remains secure, so local-only use is unaffected.
Compliance Impact

This vulnerability could lead to unauthorized data access or exposure, potentially violating GDPR's data protection requirements or HIPAA's safeguards for protected health information if sensitive data is processed via the API.

Mitigation Strategies

Upgrade Jan to a version containing the fix (commit 3e1c1e7 or later). Avoid binding the local API server to 0.0.0.0 unless necessary. Ensure the Trusted Hosts allowlist is properly configured and enforced. Disable CORS if not required and verify the CORS toggle functionality.

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