CVE-2026-81098

The Telnyx MCP server (packages/mcp-server/src/http.ts) exposed its HTTP transport on the root path with a listener bound to all network interfaces and did not require a caller credential, parsing authentication headers in a mode that tolerated their absence. As a result, an unauthenticated caller who could reach the exposed port could complete initialization and dispatch tools, and dispatch forwarded the server's own stored credentials - the Telnyx API key, client secret, and code-execution key - to the upstream endpoint, letting the attacker act with those credentials. This is a missing-authentication flaw (CWE-306) rated critical at CVSS 4.0 9.3, with high confidentiality and integrity impact. Anyone running the Telnyx MCP server with the HTTP transport reachable on a non-loopback interface is affected; the current code defaults the host to loopback and requires and enforces a server API key in middleware. No public proof-of-concept or confirmed exploitation is known, and EPSS estimates about a 0.5% probability of exploitation within 30 days.

What to do: Update to the current Telnyx MCP server code, which defaults the HTTP host to loopback and requires and enforces a server API key in middleware (the advisory does not name a specific fixed version). Until upgraded, bind the MCP HTTP transport to loopback only or restrict the port with firewall rules, and review access logs for tool-dispatch requests that arrived without credentials. If the port may have been reachable by untrusted parties, rotate the stored Telnyx API key, client secret, and code-execution key.