lemmy_defederate

THE RISK

Critical Risk

Why lemmy_defederate needs a policy

This tool purges (irreversibly deletes) cached content and severs federation relationships. While marked admin-only and queued, the capability to permanently delete federated instance data and sever inter-instance connections constitutes a destructive action with high blast radius if misconfigured or misused.

From the tool's definition Defederate from a remote instance (block + purge cached content) - the 'purge cached content' phrase indicates irreversible deletion of data, and defederation is a destructive network action that cannot be easily undone.

Risk signalsAdmin/system-level operation

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

POLICY

How to control lemmy_defederate

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 lemmy_defederate:

policy.json

{
  "version": "1",
  "default": "deny",
  "hide": [
    "lemmy_defederate"
  ]
}

lemmy_defederate disappears from the agent's tool list entirely, and any attempt to call it is denied. The rest of the server keeps working.

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.

RESTRICT THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

Critical-risk tools in Crow → Every critical-risk tool this server exposes, in one view.
All critical-risk MCP tools → Every critical-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Blast radius → How much damage one compromised or confused agent can do — and how to bound it.
Tool call approval → Approval gates on individual tool calls: auto-allow, prompt, or deny.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about lemmy_defederate

What does the lemmy_defederate tool do? +

Defederate from a remote instance (block + purge cached content). Admin-only; QUEUED. It is categorised as a Destructive tool in the Crow MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.

How do I enforce a policy on lemmy_defederate? +

Register the Crow MCP server in PolicyLayer and add a rule for lemmy_defederate: 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 lemmy_defederate? +

lemmy_defederate is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.

Can I rate-limit lemmy_defederate? +

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

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

lemmy_defederate 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.

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