Unified stop: whale requires container_id; ctfd-owl/k8s require challenge_id.
AI agents invoke stop_container to trigger actions in CTFd MCP 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.
This is an Execute action because it runs/triggers an external operation (container termination) whose effects depend directly on the arguments supplied by the caller. It is not Destructive because stopping a container is reversible (it can be restarted). The high severity reflects that in a CTF context, stopping containers could disrupt active challenges, competitors' work, or infrastructure.
From the tool's definition Tool stops containers ('stop_container') which are external operations with effects dependent on the provided container_id or challenge_id argument. Stopping a container terminates running processes and workloads.
Documented attack patterns abuse exactly the kind of access stop_container gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and CTFd MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for stop_container:
{
"version": "1",
"default": "deny",
"tools": {
"stop_container": {
"limits": [
{
"counter": "stop_container_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}stop_container 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.
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Unified stop: whale requires container_id; ctfd-owl/k8s require challenge_id. It is categorised as a Execute tool in the CTFd MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the CTFd MCP Server MCP server in PolicyLayer and add a rule for stop_container: 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 CTFd MCP Server. Nothing to install.
stop_container is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the stop_container 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 stop_container. 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.
stop_container is provided by the CTFd MCP Server MCP server (umbra2728/ctfd-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from CTFd MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
5 CTFd MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.