add_user_to_group

THE RISK

Medium Risk

Why add_user_to_group needs a policy

This tool modifies user group associations, which is a Write-category operation (creates or modifies data reversibly). While it has admin-only restrictions, misuse could grant unauthorized users inappropriate group access, permissions, or visibility to resources, affecting multiple users' access controls.

From the tool's definition Tool description explicitly states 'Add a user to a group' - this creates or modifies group membership, a reversible administrative action. The 'ADMIN ONLY' restriction indicates it's a privileged operation that modifies system state.

Risk signalsAdmin/system-level operation

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

POLICY

How to control add_user_to_group

PolicyLayer is an MCP gateway — it sits between your AI agents and Open WebUI MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for add_user_to_group:

policy.json

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

add_user_to_group 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.

Create a free account and register Open WebUI MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about add_user_to_group

What does the add_user_to_group tool do? +

Add a user to a group. ADMIN ONLY. It is categorised as a Write tool in the Open WebUI 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 add_user_to_group? +

Register the Open WebUI MCP Server MCP server in PolicyLayer and add a rule for add_user_to_group: 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 Open WebUI MCP Server. Nothing to install.

What risk level is add_user_to_group? +

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

Can I rate-limit add_user_to_group? +

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

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

add_user_to_group is provided by the Open WebUI MCP Server MCP server (troylar/open-webui-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Open WebUI MCP Server tool call.

Start from Open WebUI MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →