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From MCP to shell: MCP auth flaws enable RCE in Claude Code, Gemini CLI and more


How MCP Authentication Flaws Enable RCE in Claude Code, Gemini CLI, and More

In this blog post, we exploit this attack surface to varying degrees of success across different applications, including Cloudflare’s use-mcp client library, Anthropic’s MCP Inspector, Claude Code, Gemini CLI, and (almost) ChatGPT itself. Since we can force arbitrary client-side JavaScript execution, any user connecting to an MCP server via the use-mcp library could have been vulnerable to exploits such as session hijacking and account takeover. As multiple tools including MCP Inspector consume this SDK, this single upstream change improved security across the entire ecosystem instantly.

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RCE

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Claude Code

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