CVE-2026-65957

Description

Helio is an MCP proxy that sits between AI agents and the tools they use. Prior to version 0.8.0, the dashboard sideband (default 127.0.0.1:3100) validated CORS request origins by matching the hostname against a private-network string prefix (10., 172.16.–172.31., 192.168.) rather than validating an IP address. A public DNS name such as 192.168.attacker.com, 10.evil.io, or 172.16.pwn.example also satisfies that prefix, so the proxy echoed the attacker origin in Access-Control-Allow-Origin. This issue has been patched in version 0.8.0.

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Weakness Type (CWE)

CWE-346 CWE-346

CWE-942 CWE-942

References

Other References

https://github.com/gethelio/helio/commit/4ca8329c38b0edbc5e4d782a4e3b0cfc5cd7782e https://github.com/gethelio/helio/pull/121 https://github.com/gethelio/helio/releases/tag/v0.8.0 https://github.com/gethelio/helio/security/advisories/GHSA-2c3r-q7gv-hp2m

Frequently Asked Questions

What is CVE-2026-65957? +

Helio is an MCP proxy that sits between AI agents and the tools they use. Prior to version 0.8.0, the dashboard sideband (default 127.0.0.1:3100) validated CORS request origins by matching the hostname against a private-network string prefix (10., 172.16.–172.31., 192.168.) rather than validating an IP address. A public DNS name such as 192.168.attacker.com, 10.evil.io, or 172.16.pwn.example also satisfies that prefix, so the proxy echoed the attacker origin in Access-Control-Allow-Origin. This issue has been patched in version 0.8.0.

How do I check if I'm vulnerable to CVE-2026-65957? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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