session_fork · Iris MCP: Risk & Policy

WHAT IT DOES

What session_fork does on Iris MCP

AI agents invoke session_fork to trigger actions in Iris 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.

WHY IT NEEDS A POLICY

Why session_fork needs a policy

This tool spawns a new terminal/session, which is an execution operation that creates an interactive shell or process environment. Forking a session into a terminal window triggers external OS-level operations and could expose a live shell for arbitrary interaction, making it an Execute-category action with high severity due to the blast radius of unrestricted terminal access.

From the tool's definition Fork a session into a new terminal window for manual interaction

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

session_fork Rate-limited

session_fork 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": {
    "session_fork": {
      "limits": [
        {
          "counter": "session_fork_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 Iris MCP, so you can run agents against it safely.

FAQ

Questions about session_fork

What does the session_fork tool do? +

Fork a session into a new terminal window for manual interaction. It is categorised as a Execute tool in the Iris MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on session_fork? +

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

What risk level is session_fork? +

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

Can I rate-limit session_fork? +

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

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

session_fork is provided by the Iris MCP server (jenova-marie/iris-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.