client_user_boot · Slack MCP: Risk & Policy

WHAT IT DOES

What client_user_boot does on Slack

AI agents invoke client_user_boot to trigger actions in Slack. 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 client_user_boot needs a policy

This tool triggers an external operation — initiating/bootstrapping a Slack client session for a user. The term 'undocumented session endpoint' raises significant concern: it may grant broad session-level access or impersonate users. It is not a simple read and not purely a data write; it executes a session initialization with potentially wide-ranging side effects.

From the tool's definition 'Boot the Slack client for a specific user (undocumented session endpoint)'

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

client_user_boot Rate-limited

client_user_boot 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": {
    "client_user_boot": {
      "limits": [
        {
          "counter": "client_user_boot_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 Slack, so you can run agents against it safely.

FAQ

Questions about client_user_boot

What does the client_user_boot tool do? +

Boot the Slack client for a specific user (undocumented session endpoint). It is categorised as a Execute tool in the Slack MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on client_user_boot? +

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

What risk level is client_user_boot? +

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

Can I rate-limit client_user_boot? +

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

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

client_user_boot is provided by the Slack MCP server (karbassi/slack-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.