CVE-2025-66401: MCP Watch Command Injection Vulnerability

CVE-2025-66401 Overview

CVE-2025-66401 is a critical Command Injection vulnerability affecting MCP Watch, a comprehensive security scanner for Model Context Protocol (MCP) servers. In versions 0.1.2 and earlier, the MCPScanner class contains a critical flaw in the cloneRepo method where user-supplied githubUrl arguments are passed directly to a system shell via execSync without proper sanitization. This allows attackers to execute arbitrary commands on the host machine by appending shell metacharacters to the URL parameter.

Critical Impact

Remote attackers can achieve full system compromise by injecting malicious shell commands through unsanitized URL input, potentially leading to data theft, system takeover, and lateral movement within the network.

Affected Products

• kapilduraphe mcp_watch versions 0.1.2 and earlier
• MCP Watch Node.js package (npm)
• Systems running MCP Watch security scanner with repository cloning functionality

Discovery Timeline

• 2025-12-01 - CVE-2025-66401 published to NVD
• 2026-02-06 - Last updated in NVD database

Technical Details for CVE-2025-66401

Vulnerability Analysis

This Command Injection vulnerability (CWE-78) exists in the MCPScanner class within the cloneRepo method. The application uses Node.js's execSync function to execute git clone operations, directly interpolating user-supplied GitHub URLs into shell commands without any input validation or sanitization. This design flaw enables attackers to break out of the intended command context and execute arbitrary system commands with the privileges of the Node.js process.

The vulnerability is particularly severe because MCP Watch is designed as a security scanning tool, meaning it may run with elevated privileges and have access to sensitive configuration files, credentials, and network resources. Successful exploitation grants attackers the ability to read, modify, or delete files, establish persistence mechanisms, and pivot to other systems on the network.

Root Cause

The root cause is improper input validation when handling the githubUrl parameter in the repository cloning functionality. The vulnerable code uses execSync from the child_process module to execute shell commands, directly concatenating user input into the command string. This allows shell metacharacters (such as ;, |, &&, $(), and backticks) to be interpreted by the shell, enabling command injection.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can supply a malicious URL containing shell metacharacters to the MCP Watch scanning endpoint. For example, a crafted URL like https://github.com/repo; malicious_command would cause the shell to execute both the intended git clone operation and the injected malicious command.

The security patch demonstrates the fix by replacing execSync with spawnSync, which avoids shell interpretation of arguments:

import * as fs from "fs";
import * as path from "path";
-import { execSync } from "child_process";
+import { spawnSync } from "child_process";
import * as tmp from "tmp";
import { Vulnerability } from "../types/Vulnerability";
import { CredentialScanner } from "./scanners/CredentialScanner";

Source: GitHub Commit Log

Detection Methods for CVE-2025-66401

Indicators of Compromise

• Unusual child process spawning from the Node.js MCP Watch application
• Shell commands containing semicolons, pipes, or backticks in repository URL parameters
• Unexpected network connections originating from the MCP Watch process
• New files or modified system configurations following MCP Watch scans

Detection Strategies

• Monitor for anomalous command-line arguments passed to git or shell processes spawned by Node.js applications
• Implement input validation alerts for URLs containing shell metacharacters (;, |, &&, `, $())
• Deploy application-level logging to capture all repository URLs submitted to MCP Watch
• Use behavioral analysis to detect command execution patterns inconsistent with legitimate git clone operations

Monitoring Recommendations

• Enable comprehensive audit logging for the MCP Watch application and underlying system
• Monitor process trees for unexpected child processes of the Node.js runtime
• Implement network traffic analysis to detect data exfiltration attempts following scanner usage
• Review application logs for malformed or suspicious GitHub URLs

How to Mitigate CVE-2025-66401

Immediate Actions Required

• Upgrade MCP Watch to a version newer than 0.1.2 that includes the security patch
• If immediate upgrade is not possible, restrict network access to the MCP Watch scanning interface
• Audit logs for any evidence of exploitation attempts using malicious URL patterns
• Review system integrity for signs of compromise if the vulnerable version was exposed to untrusted input

Patch Information

The vulnerability has been addressed in a security patch that replaces the unsafe execSync function with spawnSync, which passes arguments as an array rather than constructing a shell command string. This prevents shell metacharacter interpretation and eliminates the command injection vector.

For patch details, see the GitHub Security Advisory and the security commit.

Workarounds

• Implement a reverse proxy with URL validation rules to filter malicious characters before they reach MCP Watch
• Deploy network segmentation to isolate MCP Watch from critical infrastructure
• Use application-level input sanitization to strip or escape shell metacharacters from URL inputs
• Run MCP Watch in a containerized environment with minimal privileges to limit blast radius

# Example: Run MCP Watch in a restricted Docker container
docker run --rm \
  --read-only \
  --security-opt=no-new-privileges:true \
  --cap-drop=ALL \
  --network=internal \
  mcp-watch:latest