hash_strlen

THE RISK

Low Risk

Why hash_strlen needs a policy

This tool performs a simple introspection operation on hash data structures (likely Redis HSTRLEN or similar). It only retrieves the length of a field value without creating, modifying, deleting, or executing anything. The operation is non-destructive and returns informational data only, making it a Read category tool with low severity risk.

From the tool's definition Tool description states 'Get length of field value in hash' with arguments for key and field name, returning the 'Length of field value'. This is a read-only query operation that retrieves metadata about stored data without modification or side effects.

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

POLICY

How to control hash_strlen

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_strlen:

policy.json

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

hash_strlen 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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Rate Limiting MCP Tool Calls: A Practical Guide →
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FAQ

Questions about hash_strlen

What does the hash_strlen tool do? +

Get length of field value in hash. Args: key: The name of the key field: The field name Returns: Length of field value 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_strlen? +

Register the AWS MCP server in PolicyLayer and add a rule for hash_strlen: 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_strlen? +

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

Can I rate-limit hash_strlen? +

Yes. Add a rate_limit block to the hash_strlen 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_strlen completely? +

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

hash_strlen 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.

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