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Intermediate 20 min readModule: Module 9: CSRF, SSRF & Broken Access Control

CSRF, IDOR & Server-Side Request Forgery (SSRF)

Protect against forged cross-site requests with SameSite cookies, anti-CSRF tokens, and prevent IDOR with authorization checks.

What You Will Learn in This Lesson

  • Cross-Site Request Forgery (CSRF) and SameSite=Lax/Strict cookie protection
  • Insecure Direct Object References (IDOR) when authorization checks are missing (GET /api/user/123)
  • Server-Side Request Forgery (SSRF) cloud metadata theft prevention

Introduction & Core Concept

Broken Access Control occurs when users can act outside of their intended permissions. CSRF tricks authenticated users into executing unwanted actions on web apps where they are logged in.
WHY DOES THIS MATTER IN THE REAL WORLD?

IDOR happens when an API endpoint looks up records by ID without checking whether the requesting user actually owns that record.

IDOR Authorization Guard Pattern

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async function getInvoice(invoiceId, requestingUserId) {
  const invoice = await db.invoices.findById(invoiceId);
  // MANDATORY: Verify ownership!
  if (!invoice || invoice.userId !== requestingUserId) {
    throw new ForbiddenError("You do not have permission to view this invoice.");
  }
  return invoice;
}

Line-by-Line Technical Breakdown

1SameSite=Lax prevents browsers from sending cookies along with cross-site third-party requests.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

Intelligent Code Runner & Live Sandbox[JAVASCRIPT]
JAVASCRIPT SOURCE EDITOR
Interactive Live Code

Industry Best Practices & Professional Standards

  • Always enforce ownership authorization checks at the database query level (WHERE id = $1 AND user_id = $2).

Lesson Summary & Core Takeaways

  • Access control and SameSite cookie protections prevent unauthorized cross-site actions.