What’s Vulnerable › Vulnerabilities

CVE-2026-81098: Telnyx MCP Server through 6.83.0 Missing Authentication on Streamable HTTP Transport

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-27 · updated 2026-09-24
• Weakness: CWE-306

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.

Affected products

• team-telnyx telnyx-mcp: through 6.83.0

References

• https://github.com/team-telnyx/telnyx-node
• https://github.com/team-telnyx/telnyx-node/pull/450
• https://github.com/team-telnyx/telnyx-node/security/advisories/GHSA-46jp-xr2h-fw7h
• https://www.vulncheck.com/advisories/telnyx-mcp-server-through-6.83.0-missing-authentication-on-streamable-http-transport

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