The Telnyx MCP Server exposes its HTTP transport on all network interfaces and does not enforce caller authentication when processing requests. A request without any credential is accepted, the server completes initialization, dispatches tools, and forwards the server’s own stored credentials—including the Telnyx API key, client secret, and a code‑execution key—to the upstream endpoint. Consequently, an unauthenticated attacker who can reach the exposed port can execute code or otherwise manipulate the upstream system with privileged credentials, resulting in a severe breach of confidentiality and integrity.

Telnyx MCP Server is affected by this vulnerability in all releases up to and including version 6.83.0. The issue arises from the HTTP listener being bound to all interfaces and the authentication logic allowing empty headers. Users running any version of Telnyx MCP Server within that range are therefore vulnerable.

The CVSS score of 9.3 categorizes this flaw as critical, and while EPSS is not available, the lack of authentication on a widely exposed service indicates a likely exploitation vector from external networks. The vulnerability is not listed in the CISA KEV catalog, but the exposure of privileged credentials to an unauthenticated caller elevates its impact dramatically. Attackers could remotely send HTTP requests to the MCP Server’s root path, acquire the embedded credentials, and use them to subvert the upstream endpoint. The high severity and ease of exploitation underscore the need for immediate remediation.