What happened
NVD published CVE-2026-66005 (CVSS 6.4, Medium) on 2026-07-24, detailing a CORS misconfiguration in Jan's local API server that undermines trusted-host restrictions via a wildcard-with-credentials pattern.
Why it matters
Local-first LLM applications increasingly expose OpenAI-compatible APIs and MCP tool-invocation surfaces on local networks; a CORS bypass here allows any co-located attacker (e.g., on shared Wi-Fi) or a malicious webpage via DNS rebinding to silently invoke a user's local model and MCP tools and exfiltrate the responses.
Attack vector
The local API server's CORS handling replaces user-configured trusted hosts with a wildcard that reflects arbitrary origins with credentials, allowing network-adjacent attackers (or attackers using DNS rebinding) to reach the unauthenticated OpenAI-compatible API to perform inference, enumerate models, invoke MCP tools, and read cross-origin responses.
Affected systems
Jan (jan.ai local LLM application) through 0.8.4, fixed in commit 3e1c1e7
Mitigation
Upgrade to the version containing fix commit 3e1c1e724f696620d89bb4a9cc18a380e0753757; avoid binding the local API server to 0.0.0.0 on untrusted networks.