set_variable · MCP MySQL Server MCP: Risk & Policy

WHAT IT DOES

What set_variable does on MCP MySQL Server

AI agents invoke set_variable to trigger actions in MCP MySQL Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why set_variable needs a policy

Setting MySQL system variables modifies server runtime behavior (e.g., sql_mode, max_connections, innodb settings). This is not a simple write to user data but an execution-level operation that affects server configuration and can have broad system-wide effects. It is reversible in theory but can destabilize the server or bypass security controls, warranting high severity.

From the tool's definition Set a MySQL system variable

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_variable Rate-limited

set_variable stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "set_variable": {
      "limits": [
        {
          "counter": "set_variable_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about set_variable

What does the set_variable tool do? +

Set a MySQL system variable. It is categorised as a Execute tool in the MCP MySQL Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on set_variable? +

Register the MCP MySQL Server MCP server in PolicyLayer and add a rule for set_variable: 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 MCP MySQL Server. Nothing to install.

What risk level is set_variable? +

set_variable is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit set_variable? +

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

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

set_variable is provided by the MCP MySQL Server MCP server (kami2k1/mcp-mysql). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.