CRLF Injection in TypeScript-based ERP: Best 7 Ways to Prevent It

In today’s digital era, ERP applications are increasingly built using TypeScript for better scalability and type safety. However, these benefits don’t automatically protect against classic web vulnerabilities like CRLF Injection. In this blog, we’ll break down how CRLF Injection in TypeScript-based ERP works, demonstrate it with real code examples, and show you how to secure your ERP application like a pro.

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What is CRLF Injection?

CRLF stands for Carriage Return (CR, \r) and Line Feed (LF, \n). Together, they represent the end of a line in HTTP headers. A CRLF Injection occurs when an attacker injects these characters into HTTP responses to manipulate the header and split it into two responses — leading to:

• HTTP response splitting
• Web cache poisoning
• Cross-site scripting (XSS)

When TypeScript-based ERP systems fail to sanitize user inputs, they become a prime target for such injections.

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Why TypeScript-Based ERPs Are Vulnerable

TypeScript apps often rely on libraries like Express or NestJS, which delegate trust to middleware for sanitization. When that’s missing or improperly configured, CRLF injection vulnerabilities can sneak in — especially when rendering dynamic responses or logs based on user input.

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CRLF Injection Coding Example in TypeScript (Express.js)

Let’s consider a typical ERP route in Express where an admin user dynamically sets a header based on request input:

import express from 'express';
const app = express();

app.get('/download', (req, res) => {
  const filename = req.query.filename;
  res.setHeader('Content-Disposition', `attachment; filename=${filename}`);
  res.send('File downloaded.');
});

Malicious Input:

filename=report.pdf%0D%0ASet-Cookie:%20sessionId=attacker

Resulting Response Headers:

Content-Disposition: attachment; filename=report.pdf
Set-Cookie: sessionId=attacker

⚠️ Dangerous Behavior: This leads to HTTP Response Splitting and potential session hijacking.

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How to Prevent CRLF Injection in TypeScript ERP

1. Validate and Sanitize All User Inputs

Use validation libraries like class-validator or sanitize inputs manually.

import { validate } from 'class-validator';

function sanitizeInput(input: string): string {
  return input.replace(/[\r\n]/g, '');
}

2. Use Framework-Specific Security Libraries

Frameworks like NestJS allow global pipes for sanitization and validation.

@Query('filename', new ParseFilenamePipe())
filename: string

3. Avoid Directly Using User Input in HTTP Headers

const safeFilename = sanitizeInput(req.query.filename as string);
res.setHeader('Content-Disposition', `attachment; filename=${safeFilename}`);

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Real-World Example: Logging Vulnerability in ERP

Many ERP systems log user actions. Here’s a common pattern that could go wrong:

logger.info(`User download request: ${req.query.filename}`);

Attack:

filename=report.pdf%0A[WARNING]:%20System%20Compromised

Result:

[INFO]: User download request: report.pdf
[WARNING]: System Compromised

Log injection can be used to confuse administrators or hide malicious activities.

Fix:

function escapeLogs(input: string): string {
  return input.replace(/[\r\n]/g, '').replace(/[\[\]]/g, '');
}

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🖼️ Screenshot of Website Vulnerability Scanner:

Our free tool automatically flags potential CRLF injection points and shows affected parameters in ERP routes.

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More Prevention Tips for Developers

4. Use CSP (Content Security Policy) Headers

Even if a CRLF leads to XSS, a good CSP can mitigate it.

res.setHeader("Content-Security-Policy", "default-src 'self'; script-src 'self';");

5. Don’t Trust Query Params or URL Fragments

// BAD
res.setHeader("Location", `/redirect?to=${req.query.redirectTo}`);

// BETTER
const safeURL = new URL(req.query.redirectTo, 'https://yourdomain.com');
res.setHeader("Location", safeURL.pathname);

6. Use Built-In Encoding Libraries

Use Node’s built-in libraries or packages like encode-url:

import encodeUrl from 'encodeurl';

const safeRedirect = encodeUrl(req.query.redirectTo as string);

7. Monitor Logs for Split Headers

Configure your logging service to alert on suspicious line breaks.

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🖼️ Screenshot of Vulnerability Report to check Website Vulnerability:

This helps CISOs and developers quickly identify and remediate vulnerable points.

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Related Posts You Shouldn’t Miss

If you found this post helpful, you’ll also love:

• 🔗 Prevent XSSI Attack in TypeScript ERP
• 🔗 Prevent OAuth Misconfiguration in TypeScript
• 🔗 Detecting SQL Injection in OpenCart
• 💬 Have questions or want a security assessment? Contact us here

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Bonus: Fixing SSRF Vulnerability in Laravel ERP Systems

Working on other platforms as well? Don’t miss this helpful guide on our sister website:

• 🔐 Fix SSRF Vulnerability in Laravel Securely

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Final Thoughts

CRLF Injection in TypeScript-based ERP applications is often underestimated but can lead to serious issues like session hijacking, log spoofing, or even full application compromise. By following the 7 best practices and using tools like ours for Website Security check, you can harden your ERP systems against such attacks.

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