Open (or reuse) a WebSocket subscription that streams new SMS for the authenticated user. Each incoming SMS is pushed as an MCP
AI agents call subscribe_to_messages to retrieve information from SimRelay MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves incoming SMS messages in real-time via WebSocket subscription. While it provides access to message data that could be sensitive, it performs no write, delete, or execute operations.
From the tool's definition Tool name 'subscribe_to_messages' and description 'streams new SMS for the authenticated user' and 'Each incoming SMS is pushed' indicate retrieval of data without modification.
Attacks that exploit this kind of access
Open (or reuse) a WebSocket subscription that streams new SMS for the authenticated user. Each incoming SMS is pushed as an MCP. It is categorised as a Read tool in the SimRelay MCP Server MCP Server, which means it retrieves data without modifying state.
Register the SimRelay MCP Server MCP server in PolicyLayer and add a rule for subscribe_to_messages: 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 SimRelay MCP Server. Nothing to install.
subscribe_to_messages 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 subscribe_to_messages 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 subscribe_to_messages. 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.
subscribe_to_messages is provided by the SimRelay MCP Server MCP server (simrelay/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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