I Built MCP Servers in Rust. Here Are the 5 Security Mistakes I See in Every Deployment.

Thirty CVEs in sixty days. That's the count for MCP server vulnerabilities filed between January and March 2026. One of them scored CVSS 9.6 — a remote code execution that affected 437,000+ installations. I've been building MCP servers in Rust for the past year. I designed the security layer for a spec-driven development CLI that uses MCP to orchestrate AI agents. I've also watched the ecosystem grow from a few experimental servers to something enterprises are deploying in production. The security posture of most deployments terrifies me. Here are the five mistakes I see everywhere. 1. Static API Keys in Environment Variables The Astrix Security report found that 53% of MCP servers authenticate with static, long-lived secrets. API keys in .env files, personal access tokens passed as environment variables. Only 8.5% use OAuth. I get why. The MCP quickstart guides show you how to set API_KEY=mytoken123 and move on. It works. It's fast. And it means that anyone who gains read access to yo