cache_cas · Awslabs Valkey MCP: Risk & Policy

WHAT IT DOES

What cache_cas does on Awslabs Valkey

AI agents use cache_cas to create or update resources in Awslabs Valkey — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Awslabs Valkey environment.

WHY IT NEEDS A POLICY

Why cache_cas needs a policy

This tool creates or modifies data in the cache conditionally (Write category). The severity is medium because while the operation is reversible and scoped to cache values, misuse could corrupt application state or cause race conditions if an agent repeatedly overwrites critical cached data. It does not delete data (not Destructive), execute arbitrary code (not Execute), or move money (not Financial).

From the tool's definition Tool name 'cache_cas' and description 'Set a value using CAS (Check And Set)' indicate a conditional write operation that modifies data in the cache.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

cache_cas Rate-limited

cache_cas stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "cache_cas": {
      "limits": [
        {
          "counter": "cache_cas_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Awslabs Valkey, so you can run agents against it safely.

FAQ

Questions about cache_cas

What does the cache_cas tool do? +

Set a value using CAS (Check And Set). It is categorised as a Write tool in the Awslabs Valkey MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on cache_cas? +

Register the Awslabs Valkey MCP server in PolicyLayer and add a rule for cache_cas: 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 Awslabs Valkey. Nothing to install.

What risk level is cache_cas? +

cache_cas is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit cache_cas? +

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

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

cache_cas is provided by the Awslabs Valkey MCP server (awslabs.valkey-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.