CVE-2026-81098
Received Received - Intake

MCP Server Authentication Bypass in Telnyx

Publication date: 2026-08-27

Last updated on: 2026-08-27

Assigner: VulnCheck

Description
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.

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Meta Information

Published
2026-08-27
Last Modified
2026-08-27
Generated
2026-08-27
AI Q&A
2026-08-27
EPSS Evaluated
N/A
NVD
CVE-2026-81098
EUVD
EUVD-2026-67026

Affected Vendors & Products

Showing 3 associated CPEs
Vendor Product Version / Range
telnyx mcp_server *
telnyx mcp_server 6.83.0
telnyx node_js_sdk *

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-306 The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.

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Executive Summary

The Telnyx MCP server had a flaw where it exposed its HTTP transport on all network interfaces without requiring caller authentication. The server accepted requests without credentials, processed them, and forwarded the server's own stored credentials (API key and client secret) to upstream endpoints. This allowed unauthenticated users to execute code with elevated privileges.

Detection Guidance

Check if the Telnyx MCP server is listening on all interfaces without authentication. Use commands like 'netstat -tulnp | grep <port>' or 'ss -tulnp | grep <port>' to identify open ports. Verify if the server responds to HTTP requests on the root path without requiring credentials.

Impact Analysis

An attacker could exploit this to gain unauthorized access to the Telnyx MCP server, execute arbitrary code, or access sensitive data. Since the server's credentials were forwarded automatically, attackers could perform actions as the server itself, potentially leading to data breaches or system compromise.

Compliance Impact

This vulnerability could lead to unauthorized data access or exfiltration, violating GDPR's data protection requirements and HIPAA's safeguards for protected health information. Non-compliance may result in legal penalties, fines, or reputational damage.

Mitigation Strategies

Update the Telnyx MCP server to the latest version where the host defaults to loopback and requires a server API key. Restrict network access to the server using firewalls to allow only trusted sources. Ensure middleware enforces authentication for all requests.

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