lock_sim · SimRelay MCP Server MCP: Risk & Policy

WHAT IT DOES

What lock_sim does on SimRelay MCP Server

AI agents use lock_sim to create or update resources in SimRelay MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your SimRelay MCP Server environment.

WHY IT NEEDS A POLICY

Why lock_sim needs a policy

The lock_sim tool modifies the state of a SIM resource by acquiring an exclusive lock that prevents other users/agents from accessing it. This is a reversible state change (locks expire automatically per the TTL mechanism), making it a Write operation rather than destructive. However, the severity is high because locking a SIM could prevent legitimate users from sending/receiving messages, disrupting communications.

From the tool's definition Acquire an exclusive lock on a SIM so other users/agents cannot send or read messages on it.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

lock_sim Rate-limited

lock_sim 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.

View as policy code

policy.json

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

LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about lock_sim

What does the lock_sim tool do? +

Acquire an exclusive lock on a SIM so other users/agents cannot send or read messages on it. Locks expire automatically after the server-configured TTL (typically a few minutes). Use the integer hosted_sim_id from list_sims. It is categorised as a Write tool in the SimRelay MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on lock_sim? +

Register the SimRelay MCP Server MCP server in PolicyLayer and add a rule for lock_sim: 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 SimRelay MCP Server. Nothing to install.

What risk level is lock_sim? +

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

Can I rate-limit lock_sim? +

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

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

lock_sim is provided by the SimRelay MCP Server MCP server (simrelay/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.