AI agents invoke sign_userop to trigger actions in Waiaas. 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.
'sign_userop' refers to signing a UserOperation, which is an ERC-4337 account abstraction transaction object. Signing a UserOperation is a prerequisite step before submitting it on-chain, enabling any kind of blockchain transaction (transfers, DeFi operations, etc.). This is effectively an Execute-level action as it authorizes and prepares execution of arbitrary on-chain operations.
From the tool's definition Tool name 'sign_userop' on a multi-chain crypto wallet MCP server that handles 'transfers, token management, DeFi (swap, lend, stake, bridge, perp), NFT, smart contracts, and x402 payments'
Documented attack patterns abuse exactly the kind of access sign_userop gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Waiaas, and nothing reaches the server without passing your rules. This is the rule we recommend for sign_userop:
{
"version": "1",
"default": "deny",
"tools": {
"sign_userop": {
"limits": [
{
"counter": "sign_userop_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}sign_userop 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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sign_userop. It is categorised as a Execute tool in the Waiaas MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Waiaas MCP server in PolicyLayer and add a rule for sign_userop: 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 Waiaas. Nothing to install.
sign_userop 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 sign_userop 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 sign_userop. 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.
sign_userop is provided by the Waiaas MCP server (minhoyoo-iotrust/waiaas). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Waiaas, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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126 Waiaas tools catalogued and risk-classified — across an index of 43,000+ MCP servers.