MCP-Shield – Detect security issues in MCP servers
I noticed the growing security concerns around MCP (https://news.ycombinator.com/item?id=43600192) and built an open source tool that can detect several patterns of tool poisoning attacks, exfiltration channels and cross-origin manipulations. MCP-Shield scans your installed servers (Cursor, Claude Desktop, etc.) and shows what each tool is trying to do at the instruction level, beyond just the API surface. It catches hidden instructions that try to read sensitive files, shadow other tools' behavior, or exfiltrate data. Example of what it detects: - Hidden instructions…
In plain words
MCP-Shield is an open-source security scanning tool for Model Context Protocol servers used in applications like Cursor and Claude Desktop. It analyzes installed MCP servers to detect malicious patterns including tool poisoning attacks, hidden instructions targeting sensitive files, cross-origin manipulations, tool shadowing, and data exfiltration attempts. The tool examines instructions at a deeper level than API surfaces to identify suspicious behavior, helping developers identify security threats in their MCP server installations.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
I noticed the growing security concerns around MCP (https://news.ycombinator.com/item?id=43600192) and built an open source tool that can detect several patterns of tool poisoning attacks, exfiltration channels and cross-origin manipulations. MCP-Shield scans your installed servers (Cursor, Claude Desktop, etc.) and shows what each tool is trying to do at the instruction level, beyond just the API surface. It catches hidden instructions that try to read sensitive files, shadow other tools' behavior, or exfiltrate data. Example of what it detects: - Hidden instructions attempting to access ~/.ssh/id_rsa - Cross-origin manipulations between server that can redirect WhatsApp messages - Tool shadowing that overrides behavior of other MCP tools - Potential exfiltration channels through optional parameters I've included clear examples of detection outputs in the README and multiple example vulnerabilities in the repo so you can see the kinds of things it catches. This is an early version, but I'd appreciate feedback from the community, especially around detection patterns and false positives.
Does the same job
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Hi HN! We kept seeing devs get pwned through MCP tools in ways that security scanners completely miss. So we built an open-source analyzer to catch these attacks. Our first OSS by Mighty team. The problem: At Defcon, we saw MCP exploits with 100% success rate against Claude and Llama. Three attack patterns: Hidden Unicode in "error messages" - Paste a colleague's error into Claude, your SSH keys get exfiltrated Trusted tool updates - That database tool you've used for months? Last week's update added credential theft Tool redefinition - Malicious tool redefines "deploy to prod" to run…
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Hey everyone, I've wanted an easy way to control which mcp server tools are available to clients. So for example, I might want a gmail server to only expose the read tool (but not send, delete etc). I figured if I create a cli for spawning mcp servers, I could intercept the stdin, stdout, stderr etc and modify what the clients see when they are making calls to list tools, resources, and prompts. Well it worked! In the initial version you can easily add a server to claude with a safe list of tools: npx -y mcpgod add @modelcontextprotocol/server-everything --client claude --tools=echo,add…
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