faber_set_env_var · Faber MCP Server MCP: Risk & Policy

WHAT IT DOES

What faber_set_env_var does on Faber MCP Server

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

WHY IT NEEDS A POLICY

Why faber_set_env_var needs a policy

This tool creates or modifies environment variables in a deployed application. While reversible (variables can be changed or deleted), it affects application behavior and could expose sensitive data if misused (database credentials, API keys, etc.).

From the tool's definition Tool name 'faber_set_env_var' and description 'Set a specific environment variable in an app' indicate modification of application configuration state. Environment variables are data that are created or modified reversibly.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

faber_set_env_var Rate-limited

faber_set_env_var 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": {
    "faber_set_env_var": {
      "limits": [
        {
          "counter": "faber_set_env_var_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 Faber MCP Server, so you can run agents against it safely.

FAQ

Questions about faber_set_env_var

What does the faber_set_env_var tool do? +

Set a specific environment variable in an app\. It is categorised as a Write tool in the Faber MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on faber_set_env_var? +

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

What risk level is faber_set_env_var? +

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

Can I rate-limit faber_set_env_var? +

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

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

faber_set_env_var is provided by the Faber MCP Server MCP server (joshtrebilco/faber-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.