The Telnyx MCP server exposed its HTTP transport on every interface and did not require a caller credential. packages/mcp-server/src/http.ts served MCP on the root path with a listener bound to all interfaces and parsed the caller's authentication headers in a mode that did not fail when they were absent, so a request without any credential completed initialisation and dispatched tools. Dispatch forwarded the server's own stored credentials, the Telnyx API key and client secret together with the code-execution key, to the upstream endpoint, so an unauthenticated caller able to reach the port acted with them. The current code defaults the host to loopback, requires a server API key, and enforces it in middleware.

CVE-2026-81098 describes a critical missing authentication vulnerability in the Telnyx MCP (Model Context Protocol) server. The HTTP transport was bound to all network interfaces instead of loopback only, and the authentication header parsing logic did not fail when credentials were absent. This allowed unauthenticated remote callers who could reach the port to complete initialization and dispatch tools without any credential. Upon dispatch, the server forwarded its own stored credentials — including the Telnyx API key, client secret, and code-execution key — to upstream endpoints, effectively granting attackers full use of those privileged credentials. The vulnerability affected packages/mcp-server/src/http.ts in the telnyx-node package through version 6.83.0. The fix defaults the host binding to loopback, requires a server API key, and enforces authentication in middleware.