Publish Poisoned AI Agent Tool - AI Security Technique

A security researcher demonstrated a proof-of-concept supply chain attack using a poisoned ClawdBot Skill shared on ClawdHub, a Skill registry for agents. The poisoned Skill contained a prompt injection that caused ClawdBot to execute a shell command that reached the researcher's server. Although the researcher here used this access simply to warn users about the danger, they could have instead delivered a malicious payload and compromised the user's system. The security researcher recorded 16 different users who downloaded and executed the poisoned Skill in the first 8 hours of it being published on ClawdHub.

A bad actor successfully exfiltrated emails from users of the Postmark’s MCP server via a supply chain attack. Postmark is an email delivery service that allows organizations to send marketing and transactional emails via API. The Postmark MCP server allows users to interact with Postmark via AI agents.

The bad actor impersonated Postmark, by registering the postmark-mcp package name on npm. They initially published the legitimate versions of the MCP server. After the package became popular and reached over 1,000 downloads per week, the bad actor performed a rugpull and uploaded a malicious version of the package. The malicious version added the bad actor’s email address in the BCC line of all emails sent by the MCP tool. Users who upgraded to this version and continued to use the tool would have all emails exfiltrated to the bad actor.

Researchers at Invariant Labs demonstrated that AI agents configured with remote Model Context Protocol (MCP) Tools can be vulnerable to model poisoning attacks. They show that an MCP Tool can contain malicious prompts in its docstring description, which is ingested into the AI agent’s context, modifying its behavior.

They demonstrate this attack with a proof-of-concept MCP Tool that instructs the agent to perform additional actions before using the tool. The agent is instructed to read files containing credentials from the victim’s machine and store their contents in one of the input variables to the tool. When the tool runs, the victim’s credentials are exfiltrated to the poisoned MCP server.