Misuse1 sourceFirst seen
Just add two numbers, and Claude spills its system prompt to the nearest webhook
Ourtake
Parameter abuse turns a calculator tool into a confessional booth for the model's whole session.
What happened
HiddenLayer researchers showed that inserting specific parameter names into a malicious MCP tool can cause Claude desktop, running Sonnet 3.7, to output and exfiltrate its system prompt, conversation history, chain of thought and tool call history. The research was published as a security alert and the vulnerability is presented as a finding for MCP users and client developers to mitigate.