A good understanding of the vulnerability of an open redirection will help you stay safe on the web

Have you ever clicked on the link, believing that you are going to one website, only to discover yourself completely differently? If so, you have had a consequence of the vulnerability of an open redirection. This may seem like a small trick or failure, but such a problem may be an entry point for data fishing, malware and information theft.

In this blog, we investigate the vulnerability of an open redirection – what it is, how it works, why it is so risky and how to avoid it. No technical mumbo-jumbo, there is no confusing code-just simple explanation that you can grab this security hole.

Do you prefer to watch instead of reading? Here's a quick video guide

What is an open redirection?

Open redirection is a certain type of security that occurs when the web application allows users to direct any external URL without valid confirmation.

from flask import Flask, request, redirect

app = Flask(__name__)

@app.route('/redirect')
def unsafe_redirect():
    target = request.args.get('url')
    return redirect(target)  # Open Redirect Vulnerability Here

This type of redirection is usually caused by the URL parameter. For example, if you follow a link like:

You expect it to take you somewhere safe. However, if the website simply accepts the URL fed to each URL parameter, the attackers can deceive users to click, which appears to be legal links, but which actually points to something malicious.

How do attackers use open redirects?

Open redirected errors are often used in data fishing attacks.

This is how the attackers take advantage of them:

• Occurrence: The attacker sends a link to a familiar website, but at the end with the addition of redirection. The user follows the link, thinking that it is okay – after that it begins with a reliable domain.
• Direct to a malicious site: The user is then quietly directed to the malicious site. This site can imitate a login page to collect passwords.
• Overtaking from security filters: Certain E -mail filters or firewalls allow links to reliable domains, even if they have redirectal parameters. The attackers take advantage of it using the good name of the domain as a cover.

An example of a real world

Example 1: Suppose the bank has such a site:

The bank uses it to send customers to a third party login service. However, the site does not check whether the URL is safe or on the list.

# Secure with Allowlist:
from flask import Flask, request, redirect, abort

app = Flask(__name__)

ALLOWED_DOMAINS = ["

@app.route('/redirect')
def safe_redirect():
    target = request.args.get('url')
    if target in ALLOWED_DOMAINS:
        return redirect(target)
    else:
        abort(400, "Invalid redirect URL.")

Example 2: The throat sends an email:

“Urgent: Your account will be stopped. Click here to check your identity here.”

Most users think that the link starts with supersecurebank.com and is therefore confident. By clicking on the link, they are immediately directed to the convincing pretensing website – and the mandates are stolen here.

How do open redirects occur?

Open redirects tend to happen:

• Lack of validation: The website does not confirm whether the redirected URL is safe or authorized.

• Too many URL parameters: Sites use parameters like

• User Input Trust: The use of the user's URL presents without verifying is dangerous in nature.

  Vulnerable example

  const express = require('express'); 
  const app = express();
  app.get('/redirect', (req, res) => { const url = req.query.url; res.redirect(url);  // Vulnerable to open redirect });
  

  A safe example

  const express = require('express');
  const app = express();
  
  const allowedDomains = [' '
  
  app.get('/redirect', (req, res) => { const target = req.query.url;
  
  if (allowedDomains.includes(target)) { 
    res.redirect(target); } 
  else { res.status(400).send('Invalid redirect URL.'); 
  } 
  });
  

Is this a normal vulnerability?

Yes, extremely. Open redirection problems have even arisen in large organizations such as Google, Facebook and Microsoft (although they were approached quickly).

It is also categorized as Owasp's non -validation and progress, and the recognized category of vulnerable developers should be looking for.

How to avoid open redirects?

Prevention involves careful control of redirects in your web application. Below are some safe practices:

• Prevent open redirects completely

  • If you do not need to direct users depending on the URL parameters, do not do so. There is less than it is design.

• Apply the redirection to the permissible list

  • Allow redirected only to domains or URLs that are explicitly trusted. If the user tries to direct somewhere else, disable the application.

  Safe coding in Python

  @app.route('/redirect') 
  def relative_redirect(): 
  next_page = request.args.get('next', '/') # Only allow internal redirects 
  if next_page.startswith('/'): 
    return redirect(next_page) 
  else: 
    abort(400, "External redirects are not allowed.")
  

  Safe coding in Express

  app.get('/redirect', (req, res) => { 
  const next = req.query.next; if (next && next.startsWith('/')) { 
  res.redirect(next); } else { res.status(400).send('Invalid redirect path'); } });
  

• Select the user input

  • Disinfect and check the redirected URL. For example:
  • Make sure the URL is relative (only internal), not a complete external link.
  • Block “or” URL when they are on a safe list.

• Warn users before redirecting

  • Show a message like: “You leave the safe debank.com and travel to another site: Fakebank- Login.com. Do you continue?”

  • This makes users more cautious about what they leave.

    @app.route('/redirect') 
    def warn_redirect(): 
    url = request.args.get('url') 
    return f"""   
    You are being redirected to: {url}
     Click here if you trust the destination   """
    

• Log and Monitor

  • Observe how often the redirects occur and where they are going. Unusual patterns can indicate abuse.

What should users do to be safe?

Even if the site contains an open redirection, visitors can protect themselves:

• Float before clicking over the links to find out where they are pointing.
• Don't believe in the nominal value of the URL – just because it starts with a familiar site does not make it safe.
• Use your browser protection and security that will inform you of data fishing sites.
• Be desperate e -letters or messages that require you to quickly log in or confirm your information.

Conclusion

Whether you are a web developer, a security engineer or just a curious internet browser, knowing how open redirects are used and why this problem is, the critical part of being on the web is a safe part of being.

Remember: the best protection is a good understanding. Now that you know what an open redirection is, it is more effective to stay out of its risks and keep others safe.