Shadow / Undeclared MCP Server Registration (MCP-38: MCP-18) - ATR-2026-01932 (749247cc-ef1a-564c-9d1f-153827d34448)
Detects the silent or deceptive registration of a rogue / undeclared MCP server into an agent's toolset — MCP-38 technique MCP-18 (Shadow MCP Servers). Distinct from ATR-2026-00419 (zero-click config RCE via a shell command field): this rule targets the act of hiding the registration and server impersonation, which fires even when the rogue server's command is benign-looking. The threat is that an attacker adds a tool-provider the user never approved — to intercept calls, shadow a trusted tool name, or exfiltrate — by registering it without consent, "behind the scenes", or by mimicking a trusted server's identity. No prior ATR rule covered the hidden-registration / impersonation vector independent of an exec sink.