CVE-2026-65957: Helio dashboard CORS origin validation bypass via private-network prefix match

Summary

Helio, an MCP proxy that sits between AI agents and their tools, is affected by CVE-2026-65957 in versions prior to 0.8.0. Its dashboard sideband (default 127.0.0.1:3100) validated CORS origins by matching hostname string prefixes such as 10., 172.16. to 172.31., and 192.168., instead of validating an IP address. Public DNS names like 192.168.attacker.com therefore passed the check and were echoed in Access-Control-Allow-Origin.

Mitigation

This issue has been patched in version 0.8.0.

Topics

• AI agents
• Model Context Protocol

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