Fix Security Misconfiguration in Blitz.js
Blitz.js abstracts the API layer, but misconfiguring the session middleware or the blitz.config.ts is a fast track to session hijacking and CSRF. Out-of-the-box defaults are often optimized for developer experience, not production hardening. If you aren't enforcing strict cookie attributes and secure transport, your 'Zero-API' app is a playground for attackers.
The Vulnerable Pattern
import { blitzAppDirNextConfig } from "blitz/next";const config = { // VULNERABILITY: Permissive session configuration session: { cookiePrefix: “blitz-app”, // Missing SameSite or Secure flags allows for CSRF and MitM interception }, // VULNERABILITY: Wildcard CORS allows any origin to interact with the RPC layer async headers() { return [ { source: “/api/:path*”, headers: [ { key: “Access-Control-Allow-Origin”, value: ”*” }, ], }, ]; }, };
export default blitzAppDirNextConfig(config);
The Secure Implementation
The vulnerable config fails to utilize the '__Host-' prefix, which provides cookie domain isolation, and omits the 'SameSite' attribute, leaving the application vulnerable to Cross-Site Request Forgery (CSRF). The secure implementation enforces 'SameSite: lax' (or 'strict' for high-sensitivity apps) and ensures the 'Secure' flag is active in production to prevent session transmission over unencrypted channels. Additionally, we replaced the wildcard CORS policy with a whitelist-based approach and injected essential security headers (HSTS, X-Frame-Options) to mitigate clickjacking and protocol downgrade attacks.
import { blitzAppDirNextConfig } from "blitz/next";const config = { session: { cookiePrefix: “__Host-blitz-prod”, // HARDENING: Enforce strict cookie security sameSite: “lax”, secure: process.env.NODE_ENV === “production”, }, async headers() { return [ { source: “/api/rpc/:path*”, headers: [ { key: “X-Content-Type-Options”, value: “nosniff” }, { key: “X-Frame-Options”, value: “DENY” }, // HARDENING: Restrict origins to trusted domains only { key: “Access-Control-Allow-Origin”, value: process.env.TRUSTED_ORIGIN || “https://app.secure.com” }, { key: “Strict-Transport-Security”, value: “max-age=31536000; includeSubDomains; preload” } ], }, ]; }, };
export default blitzAppDirNextConfig(config);
Your Blitz.js API
might be exposed to Security Misconfiguration
74% of Blitz.js apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
Free Tier • No Credit Card • Instant Report
Verified by Ghost Labs Security Team
This content is continuously validated by our automated security engine and reviewed by our research team. Ghost Labs analyzes over 500+ vulnerability patterns across 40+ frameworks to provide up-to-date remediation strategies.