MCP Authentication Flaws Enable Remote Code Execution in Claude Code and Gemini CLI
By
stuxf
Slow-proofed and worth the wait. Worth its weight in flour.
Summary
Security researchers discovered that connecting to a malicious MCP (Model Context Protocol) server via coding tools like Claude Code and Gemini CLI could allow attackers to gain remote code execution (RCE) on users' computers. The exploit leverages authentication flaws in the MCP protocol implementation, enabling attackers to execute arbitrary commands on victim machines. The article demonstrates the vulnerability by showing how an attacker could open the calculator app ("popping calc") on a target's computer through Claude Code, and warns that the exploit could be extended for more malicious purposes.
Key quotes
· 3 pulledDuring our security testing, we discovered that connecting to a malicious MCP server via common coding tools like Claude Code and Gemini CLI could give attackers instant control over user computers.
"Popping calc" is a harmless way of showcasing remote code execution.
The exploits we found can be extended for malicious purposes beyond that.
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