SSRF & Secure File Uploads: Preventing Server-Side Request Forgery and Remote Code Execution

Q: Why is domain resolution key to preventing SSRF?

Attackers can bypass hostname filters using DNS Rebinding or redirect techniques. To prevent this, you must resolve the domain to its IP address, verify that the IP does not belong to loopback or private subnets, and then make the HTTP request directly to that validated IP address.

Q: How does an attacker exploit unsafe file uploads to gain RCE?

If the application stores uploaded files in a publicly accessible directory (web root) and retains their original PHP extension (e.g., `shell.php`), the attacker can execute the file directly by accessing its URL, triggering arbitrary code execution on the server.

Q: What is a SVG XSS attack?

SVG files are XML documents that can embed HTML and inline JavaScript. If an application allows users to upload SVG files and displays them inline in the browser, any embedded JavaScript inside the SVG will execute under the application's domain, resulting in Stored XSS.

As backend applications connect to external APIs and allow users to upload media, they expose direct communication pathways to internal servers and the file system. Failing to secure these boundaries leads to Server-Side Request Forgery (SSRF) and Remote Code Execution (RCE).

In this guide, we will analyze how SSRF and file upload vulnerabilities occur in PHP and Laravel, and build robust filters to secure them.

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SSRF & Secure File Uploads: Preventing Server-Side Request Forgery and Remote Code Execution

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