AI agents invoke tools_john to trigger actions in Zebbern Kali MCP. 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.
This tool runs John the Ripper, an external password cracking program. The outcome depends entirely on what hashes are provided and what wordlists/rules are used. While not inherently destructive or financial, it executes an external operation that could be misused to crack credentials in an unauthorized context.
From the tool's definition The tool description states it will 'Execute John the Ripper password cracker.' John the Ripper is a command-line password cracking utility that runs computational operations whose effects depend on input arguments (wordlists, hash files, rules, etc.).
Documented attack patterns abuse exactly the kind of access tools_john gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Zebbern Kali MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for tools_john:
{
"version": "1",
"default": "deny",
"tools": {
"tools_john": {
"limits": [
{
"counter": "tools_john_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}tools_john 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.
Free to start. No card required.
Execute John the Ripper password cracker. It is categorised as a Execute tool in the Zebbern Kali MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Zebbern Kali MCP server in PolicyLayer and add a rule for tools_john: 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 Zebbern Kali MCP. Nothing to install.
tools_john is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the tools_john 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.
Set action: deny in the PolicyLayer policy for tools_john. 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.
tools_john is provided by the Zebbern Kali MCP server (zebbern/zebbern-kali-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 128 Zebbern Kali MCP tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
128 Zebbern Kali MCP tools catalogued and risk-classified — across an index of 42,500+ MCP servers.