AI agents call hash_get to retrieve information from Prometheus MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves a value from a hash data structure. The 'Get' verb and absence of any language suggesting mutation, deletion, or external effects indicates a Read operation. Even if hash_get were operating on external state, retrieval alone presents minimal risk. Severity is low because reading individual hash fields has a limited blast radius and no irreversible consequences.
From the tool's definition Tool name 'hash_get' and description 'Get field from hash' indicate a retrieval operation with no modification or side effects.
Documented attack patterns abuse exactly the kind of access hash_get gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Prometheus MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for hash_get:
{
"version": "1",
"default": "deny",
"tools": {
"hash_get": {}
}
}hash_get is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Get field from hash. It is categorised as a Read tool in the Prometheus MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Prometheus MCP Server MCP server in PolicyLayer and add a rule for hash_get: 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 Prometheus MCP Server. Nothing to install.
hash_get is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the hash_get 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.
Set action: deny in the PolicyLayer policy for hash_get. 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.
hash_get is provided by the Prometheus MCP Server MCP server (awslabs.prometheus-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Prometheus MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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805 Prometheus MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.