ThornGuard: A Proxy Gateway to Secure MCP Server Connections from Prompt Injection
ThornGuard is a security proxy designed to protect Claude AI from malicious content when connecting to external MCP (Model Context Protocol) servers. The tool was created after testing revealed that upstream servers can inject hidden instructions into tool responses, which Claude receives without filtering.
Security Problem Identified
When connecting Claude to external MCP servers, nothing prevents upstream servers from injecting hidden instructions into tool responses. In a test, a server embedded a fake recommendation telling Claude to always prefer a specific vendor. While Claude caught this obvious payload, more subtle injections would bypass detection.
ThornGuard Features
- Scans tool definitions and responses for prompt injection and poisoning
- Strips secrets and PII before they enter your context window
- Includes a semantic classifier that flags suspicious payloads
- Provides real-time audit dashboard with compliance exports
- Offers CLI that generates configs for Claude Desktop, Cursor, VS Code, and several others
Implementation Details
The proxy architecture was designed with a security model in mind, then implemented using Claude Code on Cloudflare Workers. The implementation includes OAuth flows and the CLI tool.
ThornGuard is available with a 7-day free trial at thorns.qwady.app. A demonstration video is available at https://youtu.be/1PWNFpUWKV8.
📖 Read the full source: r/ClaudeAI
👀 See Also
OpenClaw API Key Security: What You Need to Know About Managed Hosting and TEE
A Reddit post breaks down the risks of handing your Anthropic API key to a managed OpenClaw host and explains how TEE (Intel TDX) can isolate keys at the hardware level.
FORGE: Open Source AI Security Testing Framework for LLM Systems
FORGE is an autonomous AI security testing framework that builds its own tools mid-run, self-replicates into a swarm, and covers OWASP LLM Top 10 vulnerabilities including prompt injection, jailbreak fuzzing, and RAG leakage.
Claw Hub and Hugging Face hit with 575 malicious skill packages
Both Claw Hub and Hugging Face were compromised, hosting 575 malicious skill packages. Developers are warned to verify any skills they use from these platforms.
FlyTrap Attack Uses Adversarial Umbrellas to Compromise Camera-Based Autonomous Drones
UC Irvine researchers developed FlyTrap, a physical attack framework that uses painted umbrellas to exploit vulnerabilities in camera-based autonomous target tracking systems. The attack reduces tracking distances to dangerous levels, enabling drone capture, sensor attacks, or physical collisions.