kerberos_realm_list

THE RISK

Low Risk

Why kerberos_realm_list needs a policy

This tool queries and returns information about existing Kerberos realm configurations. It performs no modifications, deletions, or external operations. The action is purely informational, making it a Read category tool with low severity since listing configuration data poses minimal risk even if accessed by an untrusted agent.

From the tool's definition Tool name contains 'list' and description explicitly states 'List all configured Kerberos realms' — a retrieval operation with no side effects.

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

POLICY

How to control kerberos_realm_list

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

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "kerberos_realm_list": {}
  }
}

kerberos_realm_list is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

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

CAP THIS TOOL →

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EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about kerberos_realm_list

What does the kerberos_realm_list tool do? +

List all configured Kerberos realms. It is categorised as a Read tool in the Truenas MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on kerberos_realm_list? +

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

What risk level is kerberos_realm_list? +

kerberos_realm_list is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit kerberos_realm_list? +

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

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

kerberos_realm_list is provided by the Truenas MCP server (spranab/truenas-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Truenas tool call.

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

CHECK YOUR STACK →