hash_length

THE RISK

Low Risk

Why hash_length needs a policy

This is a read-only query operation that introspects a hash data structure to retrieve its field count. It has no side effects, cannot modify or delete data, and poses minimal security risk even if called with arbitrary keys.

From the tool's definition Tool returns 'Number of fields' with no modification capability. Accepts a key name and retrieves metadata about a hash structure. No data modification, deletion, or execution described.

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

POLICY

How to control hash_length

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

policy.json

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

hash_length 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 AWS — 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

Roll out MCP under one policy → Per-person scoped tokens, one central policy, and full audit across every server your team connects.
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 →
PolicyLayer vs alternatives → How deterministic, per-call MCP policy compares with gateways, identity layers, and authorisation platforms.

FAQ

Questions about hash_length

What does the hash_length tool do? +

Get number of fields in hash. Args: key: The name of the key Returns: Number of fields or error message. It is categorised as a Read tool in the AWS MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on hash_length? +

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

What risk level is hash_length? +

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

Can I rate-limit hash_length? +

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

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

hash_length is provided by the AWS MCP server (@awslabs/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every AWS tool call.

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

CHECK YOUR STACK →