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CVE-2026-81735 — startServer.ts in the mcp-http-server package of UI-TARS-desktop defaulted its listen…

Key facts

CVE-2026-81735 is a Critical (10.0) vulnerability: startServer.ts in the mcp-http-server package of UI-TARS-desktop defaulted its listen…. This entry ships a detection-only PoC and a Docker test lab.
CVE CVE-2026-81735
Severity Critical (10.0)
Detection / prevention —
PoC poc.py
Source 2026/CVE-2026-81735/

Details

English | 한국어

Description

startServer.ts in the mcp-http-server package of UI-TARS-desktop defaulted its listen address to '::' when no host was given, so startSseAndStreamableHttpMcpServer bound the Streamable HTTP and SSE MCP transports to every interface, and its authentication middleware was optional: middlewares are applied only when a caller supplies them. The @agent-infra/mcp-server-commands and @agent-infra/mcp-server-filesystem entry points call startSseAndStreamableHttpMcpServer with a host and port alone and pass no middleware, so neither server required a credential. The commands server exposes a run_command tool that hands its caller-supplied command string to promisify(child_process.exec), so any unauthenticated client able to reach the port could run arbitrary commands as the user running the server, and the filesystem server exposed its file read and write tools on the same terms. The listen default became 127.0.0.1 in commit c2ad42e3eb9b27830db41a3e6f51ca7179d9b168; the package version stayed at 1.2.4 across that change, so the boundary is the commit rather than a release.

Vulnerability Details

Property Value
CVE ID CVE-2026-81735
CVSS Score 10.0

Proof of Concept

Download

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-81735/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-2026-81735

# 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/bytedance/UI-TARS-desktop
  • https://github.com/bytedance/UI-TARS-desktop/blob/e9f3387288da4af2ad99972da2ac916cdabce093/packages/agent-infra/mcp-http-server/src/startServer.ts#L263
  • https://github.com/bytedance/UI-TARS-desktop/commit/c2ad42e3eb9b27830db41a3e6f51ca7179d9b168
  • https://github.com/bytedance/UI-TARS-desktop/pull/1918
  • https://www.vulncheck.com/advisories/ui-tars-desktop-agent-infra-mcp-servers-bind-every-interface-without-authentication-exposing-arbitrary-command-execution

Generated by PoC Generator on 2026-08-30T10:05:12.406905243

Frequently asked questions

What is CVE-2026-81735?

CVE-2026-81735 is a Critical (10.0) vulnerability: startServer.ts in the mcp-http-server package of UI-TARS-desktop defaulted its listen…. This entry ships a detection-only PoC and a Docker test lab.

How do I detect CVE-2026-81735?

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-2026-81735?

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.