CVE-2026-81098 — The Telnyx MCP server exposed its HTTP transport on every interface and did not require a…¶

Key facts

CVE-2026-81098 is a Critical (9.1) vulnerability: The Telnyx MCP server exposed its HTTP transport on every interface and did not require a…. This entry ships a detection-only PoC and a Docker test lab.


CVE	CVE-2026-81098
Severity	Critical (9.1)
Detection / prevention	—
PoC	poc.py
Source	2026/CVE-2026-81098/

Details¶

English | 한국어

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.

Vulnerability Details¶

Property	Value
CVE ID	CVE-2026-81098
Type	RCE
CVSS Score	9.1

Proof of Concept¶

Download¶

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-81098/poc.py

Usage¶

# Run PoC against target
python3 poc.py --target <TARGET_URL>

# With authentication
python3 poc.py --target <TARGET_URL> --username <USER> --password <PASS>

⚠️ Warning: This PoC is for authorized security testing only. It uses detection-only techniques and does not exploit or damage target systems.

Test Lab¶

This repository includes a Docker-based test environment with both vulnerable and patched applications.

Quick Start¶

# Clone and navigate to CVE directory
cd CVE-2026-81098

# Start both applications
docker-compose up -d

# Run tests
./run-tests.sh    # Linux/Mac
./run-tests.ps1   # Windows PowerShell

Application Endpoints¶

Application	URL	Status
Vulnerable App	http://localhost:8080	Shows vulnerability
Patched App	http://localhost:8081	Demonstrates fix

Directory Structure¶

├── README.md           # English documentation
├── README_KO.md        # Korean documentation
├── poc.py              # PoC detection script
├── docker-compose.yml  # Container orchestration
├── run-tests.sh        # Linux/Mac test runner
├── run-tests.ps1       # Windows test runner
├── vulnerable-app/     # Vulnerable version
│   ├── app.py
│   ├── Dockerfile
│   └── requirements.txt
└── patched-app/        # Fixed version
    ├── app.py
    ├── Dockerfile
    └── requirements.txt

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

Generated by PoC Generator on 2026-08-30T11:49:58.996931934

Frequently asked questions¶

What is CVE-2026-81098?¶

CVE-2026-81098 is a Critical (9.1) vulnerability: The Telnyx MCP server exposed its HTTP transport on every interface and did not require a…. This entry ships a detection-only PoC and a Docker test lab.

How do I detect CVE-2026-81098?¶

Run the detection-only PoC included with this entry against your Docker test lab to confirm whether a target is affected; pair it with your own IDS logging.

How do I block or mitigate CVE-2026-81098?¶

Upgrade to a fixed version per the vendor advisory; the NVD record lists the affected versions. Use the included PoC to verify your remediation.

For authorized security testing and research only. See the full source and NVD record.