pf_block_user

THE RISK

Medium Risk

Why pf_block_user needs a policy

Blocking a user is a reversible write action that modifies the authenticated user's account state (block list). It does not delete data or execute code, and it can be undone by unblocking. The blast radius is medium as it affects social interactions and content visibility but is not irreversible.

From the tool's definition Block an account system-wide (the authenticated user no longer sees their posts)

Documented attack patterns abuse exactly the kind of access pf_block_user gives an agent:

POLICY

How to control pf_block_user

PolicyLayer is an MCP gateway — it sits between your AI agents and Crow, and nothing reaches the server without passing your rules. This is the rule we recommend for pf_block_user:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "pf_block_user": {
      "limits": [
        {
          "counter": "pf_block_user_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

pf_block_user stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

Create a free account and register Crow — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about pf_block_user

What does the pf_block_user tool do? +

Block an account system-wide (the authenticated user no longer sees their posts). Rate-limited: 5/hour. It is categorised as a Write tool in the Crow MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on pf_block_user? +

Register the Crow MCP server in PolicyLayer and add a rule for pf_block_user: 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 Crow. Nothing to install.

What risk level is pf_block_user? +

pf_block_user is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit pf_block_user? +

Yes. Add a rate_limit block to the pf_block_user 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 pf_block_user completely? +

Set action: deny in the PolicyLayer policy for pf_block_user. 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 pf_block_user? +

pf_block_user is provided by the Crow MCP server (kh0pper/crow). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Crow tool call.

Start from Crow, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →