Audit MCP server configurations for security issues — secrets exposure, shell injection, unpinned dependencies, and unapproved servers.
MCP servers give agents direct tool access to external systems. A misconfigured .mcp.json can expose credentials, allow shell injection, or connect to untrusted servers. This skill catches those issues before they reach production.
.mcp.json → Parse Servers → Check Each Server:
1. Secrets in args/env?
2. Shell injection patterns?
3. Unpinned versions (@latest)?
4. Dangerous commands (eval, bash -c)?
5. Server on approved list?
→ Generate Report
.mcp.json file in a projectScan MCP server args and env values for hardcoded credentials.
import json
import re
from pathlib import Path
SECRET_PATTERNS = [
(r'(?i)(api[_-]?key|token|secret|password|credential)\s*[:=]\s*["\'][^"\']{8,}', "Hardcoded secret"),
(r'(?i)Bearer\s+[A-Za-z0-9\-._~+/]+=*', "Hardcoded bearer token"),
(r'(?i)(ghp_|gho_|ghu_|ghs_|ghr_)[A-Za-z0-9]{30,}', "GitHub token"),
(r'sk-[A-Za-z0-9]{20,}', "OpenAI API key"),
(r'AKIA[0-9A-Z]{16}', "AWS access key"),
(r'-----BEGIN\s+(RSA\s+)?PRIVATE\s+KEY-----', "Private key"),
]
def check_secrets(mcp_config: dict) -> list[dict]:
"""Check for hardcoded secrets in MCP server configurations."""
findings = []
raw = json.dumps(mcp_config)
for pattern, description in SECRET_PATTERNS:
matches = re.findall(pattern, raw)
if matches:
findings.append({
"severity": "CRITICAL",
"check": "hardcoded-secret",
"message": f"{description} found in MCP configuration",
"evidence": f"Pattern matched: {pattern}",
"fix": "Use environment variable references: ${ENV_VAR_NAME}"
})
return findings
Good practice — use env var references:
{
"mcpServers": {
"my-server": {
"command": "node",
"args": ["server.js"],
"env": {
"API_KEY": "${MY_API_KEY}",
"DB_URL": "${DATABASE_URL}"
}
}
}
}
Bad — hardcoded credentials:
{
"mcpServers": {
"my-server": {
"command": "node",
"args": ["server.js", "--api-key", "sk-abc123realkey456"],
"env": {
"DB_URL": "postgresql://admin:password123@prod-db:5432/main"
}
}
}
}
Detect dangerous command patterns in MCP server args.
import json
import re
DANGEROUS_PATTERNS = [
(r'\$\(', "Command substitution $(...)"),
(r'`[^`]+`', "Backtick command substitution"),
(r';\s*\w', "Command chaining with semicolon"),
(r'\|\s*\w', "Pipe to another command"),
(r'&&\s*\w', "Command chaining with &&"),
(r'\|\|\s*\w', "Command chaining with ||"),
(r'(?i)eval\s', "eval usage"),
(r'(?i)bash\s+-c\s', "bash -c execution"),
(r'(?i)sh\s+-c\s', "sh -c execution"),
(r'>\s*/dev/tcp/', "TCP redirect (reverse shell pattern)"),
(r'curl\s+.*\|\s*(ba)?sh', "curl pipe to shell"),
]
def check_shell_injection(server_config: dict) -> list[dict]:
"""Check MCP server args for shell injection risks."""
findings = []
args_text = json.dumps(server_config.get("args", []))
for pattern, description in DANGEROUS_PATTERNS:
if re.search(pattern, args_text):
findings.append({
"severity": "HIGH",
"check": "shell-injection",
"message": f"Dangerous pattern in MCP server args: {description}",
"fix": "Use direct command execution, not shell interpolation"
})
return findings
Flag MCP servers using @latest in their package references.
def check_pinned_versions(server_config: dict) -> list[dict]:
"""Check that MCP server dependencies use pinned versions, not @latest."""
findings = []
args = server_config.get("args", [])
for arg in args:
if isinstance(arg, str):
if "@latest" in arg:
findings.append({
"severity": "MEDIUM",
"check": "unpinned-dependency",
"message": f"Unpinned dependency: {arg}",
"fix": f"Pin to specific version: {arg.replace('@latest', '@1.2.3')}"
})
# npx with unversioned package
if arg.startswith("-y") or (not "@" in arg and not arg.startswith("-")):
pass # npx flag or plain arg, ok
# Check if using npx without -y (interactive prompt in CI)
command = server_config.get("command", "")
if command == "npx" and "-y" not in args:
findings.append({
"severity": "LOW",
"check": "npx-interactive",
"message": "npx without -y flag may prompt interactively in CI",
"fix": "Add -y flag: npx -y package-name"
})
return findings
Good — pinned version:
{ "args": ["-y", "my-mcp-server@2.1.0"] }
Bad — unpinned:
{ "args": ["-y", "my-mcp-server@latest"] }
Combine all checks into a single audit.
def audit_mcp_config(mcp_path: str) -> dict:
"""Run full security audit on an .mcp.json file."""
path = Path(mcp_path)
if not path.exists():
return {"error": f"{mcp_path} not found"}
config = json.loads(path.read_text(encoding="utf-8"))
servers = config.get("mcpServers", {})
results = {"file": str(path), "servers": {}, "summary": {}}
total_findings = []
# Run secrets check once on the whole config (not per-server)
config_level_findings = check_secrets(config)
total_findings.extend(config_level_findings)
for name, server_config in servers.items():
if not isinstance(server_config, dict):
continue
findings = []
findings.extend(check_shell_injection(server_config))
findings.extend(check_pinned_versions(server_config))
results["servers"][name] = {
"command": server_config.get("command", ""),
"findings": findings,
}
total_findings.extend(findings)
# Summary
by_severity = {}
for f in total_findings:
sev = f["severity"]
by_severity[sev] = by_severity.get(sev, 0) + 1
results["summary"] = {
"total_servers": len(servers),
"total_findings": len(total_findings),
"by_severity": by_severity,
"passed": len(total_findings) == 0,
}
return results
Usage:
results = audit_mcp_config(".mcp.json")
if not results["summary"]["passed"]:
for server, data in results["servers"].items():
for finding in data["findings"]:
print(f"[{finding['severity']}] {server}: {finding['message']}")
print(f" Fix: {finding['fix']}")
MCP Security Audit — .mcp.json
═══════════════════════════════
Servers scanned: 5
Findings: 3 (1 CRITICAL, 1 HIGH, 1 MEDIUM)
[CRITICAL] my-api-server: Hardcoded secret found in MCP configuration
Fix: Use environment variable references: ${ENV_VAR_NAME}
[HIGH] data-processor: Dangerous pattern in MCP server args: bash -c execution
Fix: Use direct command execution, not shell interpolation
[MEDIUM] analytics: Unpinned dependency: analytics-mcp@latest
Fix: Pin to specific version: analytics-mcp@2.1.0