john_crack · John The Ripper MCP: Risk & Policy

WHAT IT DOES

What john_crack does on John The Ripper

AI agents invoke john_crack to trigger actions in John The Ripper. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why john_crack needs a policy

This tool executes code/external operations (John the Ripper binary) with arguments that determine behavior. It is not merely reading data (Read), nor creating/modifying user data reversibly (Write). While it could be destructive in a secondary sense if used against production systems without authorization, the primary capability is executing password attacks.

From the tool's definition Tool starts password cracking with John the Ripper, supporting multiple cracking modes (wordlist, incremental, single crack).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

john_crack Rate-limited

john_crack stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "john_crack": {
      "limits": [
        {
          "counter": "john_crack_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches John The Ripper, so you can run agents against it safely.

FAQ

Questions about john_crack

What does the john_crack tool do? +

Start password cracking with John the Ripper. Supports various modes including wordlist, incremental, and single crack. It is categorised as a Execute tool in the John The Ripper MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on john_crack? +

Register the John The Ripper MCP server in PolicyLayer and add a rule for john_crack: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches John The Ripper. Nothing to install.

What risk level is john_crack? +

john_crack is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit john_crack? +

Yes. Add a rate_limit block to the john_crack rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block john_crack completely? +

Set action: deny in the PolicyLayer policy for john_crack. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides john_crack? +

john_crack is provided by the John The Ripper MCP server (schwarztim/sec-john-the-ripper-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.