AI agents call list_users to retrieve information from Open WebUI MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This is a read-only operation that queries and returns user data. While it requires admin privileges and reveals user information (which could be sensitive in some contexts), it has no side effects and cannot be exploited to modify systems or data. The 'ADMIN ONLY' restriction mitigates risk, but the sensitivity of user lists warrants medium rather than low severity.
From the tool's definition Tool name is 'list_users' and description states 'List all users in Open WebUI. ADMIN ONLY.' — this retrieves user information without modifying, deleting, or executing operations.
Risk signalsBulk/mass operation — affects multiple targets · Admin/system-level operation
Documented attack patterns abuse exactly the kind of access list_users gives an agent:
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 list_users:
{
"version": "1",
"default": "deny",
"tools": {
"list_users": {}
}
}list_users is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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List all users in Open WebUI. ADMIN ONLY. It is categorised as a Read tool in the Open WebUI MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Open WebUI MCP Server MCP server in PolicyLayer and add a rule for list_users: 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.
list_users 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 list_users 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 list_users. 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.
list_users 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.
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.
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82 Open WebUI MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.