AI agents use set_cookies to create or update resources in N Lobby MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your N Lobby MCP Server environment.
This tool writes/modifies security-critical authentication cookies, which changes the authenticated session state. While not destructive (cookies can be cleared/reset), it is a Write operation with high severity because unauthorized cookie manipulation could enable session hijacking, impersonation, or unauthorized access to school portal data.
From the tool's definition Tool name is 'set_cookies' and description states it 'Set authentication cookies for N Lobby access'. Setting cookies is a write operation that modifies authentication state.
Documented attack patterns abuse exactly the kind of access set_cookies gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and N Lobby MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for set_cookies:
{
"version": "1",
"default": "deny",
"tools": {
"set_cookies": {
"limits": [
{
"counter": "set_cookies_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_cookies 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.
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Set authentication cookies for N Lobby access. It is categorised as a Write tool in the N Lobby MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the N Lobby MCP Server MCP server in PolicyLayer and add a rule for set_cookies: 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 N Lobby MCP Server. Nothing to install.
set_cookies is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the set_cookies 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 set_cookies. 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.
set_cookies is provided by the N Lobby MCP Server MCP server (minagishl/nlobby-cli). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from N Lobby 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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28 N Lobby MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.