Exploiting SSRF with Open Redirect: A Powerful Combo for Bug Bounty Hunters

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Introduction

Server-Side Request Forgery (SSRF) vulnerabilities allow attackers to force a server to make unintended requests, often leading to internal network exposure. When combined with an open redirect, SSRF can bypass strict URL filters, escalating its impact. This article explores how to chain these vulnerabilities for maximum exploitation.

Learning Objectives

  • Understand how SSRF and open redirect vulnerabilities interact.
  • Learn techniques to bypass SSRF filters using open redirects.
  • Discover real-world exploitation strategies for bug bounty hunting.

You Should Know

1. Bypassing SSRF Restrictions with Open Redirect

Scenario: An endpoint (fetchImage.php) only allows requests to `image.example[.]com` but is vulnerable to SSRF.

Exploit URL:

example[.]com/fetchImage.php?url=image.example[.]com?redirect=127.0.0[.]1/admin

Step-by-Step Guide:

  1. Identify an open redirect vulnerability in the allowed subdomain (e.g., image.example[.]com).
  2. Craft a URL that chains the open redirect with the SSRF, tricking the server into accessing internal endpoints.
  3. Use the redirect parameter to point to sensitive internal systems (e.g., admin panels, metadata services).

2. Testing for Open Redirects

Command (cURL):

curl -v "https://image.example.com/redirect?url=https://attacker.com"

Step-by-Step Guide:

  1. Test endpoints like /redirect, /logout, or `/auth` for open redirects.
  2. Look for HTTP 3xx responses with arbitrary URLs in parameters.
  3. Verify if the server follows the redirect without validation.

3. Exploiting SSRF to Access Metadata Services (AWS/GCP)

Payload:

http://image.example.com/redirect?url=http://169.254.169.254/latest/meta-data/

Step-by-Step Guide:

  1. Use the open redirect to bypass SSRF filters.
  2. Target cloud metadata endpoints to steal IAM credentials.

3. Exfiltrate sensitive data or escalate privileges.

4. Mitigating SSRF Vulnerabilities

Recommended Fix (PHP):

$allowed_domains = ['image.example.com']; 
$url = parse_url($_GET['url']); 
if (!in_array($url['host'], $allowed_domains)) { 
die("Invalid URL"); 
}

Step-by-Step Guide:

1. Implement strict allowlists for domains.

2. Disable protocol handlers like `file://`, `gopher://`.

3. Use network-level restrictions to block internal access.

5. PortSwigger Lab Walkthrough

Lab Link: SSRF Filter Bypass via Open Redirection

Steps to Solve:

  1. Identify the SSRF endpoint (e.g., stock check feature).
  2. Find an open redirect in the allowed domain.
  3. Chain the vulnerabilities to access the admin panel.

What Undercode Say

  • Key Takeaway 1: Open redirects are often underestimated but can be critical for bypassing SSRF filters.
  • Key Takeaway 2: Bug bounty hunters should document and retain low-severity findings (like open redirects) for chaining with higher-impact vulnerabilities.

Analysis:

The combination of SSRF and open redirect demonstrates the importance of holistic security testing. While SSRF alone may seem limited, auxiliary vulnerabilities can unlock its full potential. Enterprises must adopt layered defenses, including input validation and strict allowlisting, to prevent such exploits. As cloud adoption grows, SSRF attacks targeting metadata services will become increasingly prevalent, making this a priority for penetration testers and developers alike.

Prediction

Future SSRF attacks will increasingly leverage chained vulnerabilities (like open redirects or DNS rebinding) to bypass advanced filters. Automated tools will emerge to scan for these combos, raising the bar for defensive strategies. Organizations must prioritize secure-by-design architectures to mitigate these risks.

IT/Security Reporter URL:

Reported By: Martinmarting An – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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