Bypassing Referer-based CSRF defenses

Platform: PortSwigger | Category: CSRF | Type: Lab | Difficulty: N/A | OS: N/A | Author: XESXOR | Date: 2026-08-24 | Status: Solved Techniques: Web Security Academy, CSRF

Summary

Walkthrough of the PortSwigger Web Security Academy lab Bypassing Referer-based CSRF defenses (CSRF). This lab demonstrates a csrf vulnerability and its exploitation to achieve the lab objectives.

Lab Overview

PortSwigger Web Security Academy — CSRF

This writeup is part of the XESXOR PortSwigger collection. The original lab description and solution have been preserved and reformatted for clarity.

Aside from defenses that employ CSRF tokens, some applications make use of the HTTP Referer header to attempt to defend against CSRF attacks, normally by verifying that the request originated from the application's own domain. This approach is generally less effective and is often subject to bypasses

What is Referrer header -

The HTTP Referer header (which is inadvertently misspelled in the HTTP specification) is an optional request header that contains the URL of the web page that linked to the resource that is being requested.

It is generally added automatically by browsers when a user triggers an HTTP request, including by clicking a link or submitting a form. Various methods exist that allow the linking page to withhold or modify the value of the Referer header. This is often done for privacy reasons.

Key Takeaways / Lessons

• Understanding CSRF detection and exploitation is crucial for web security.
• Always validate and sanitize user input; implement proper access controls.
• This lab is part of the PortSwigger Web Security Academy — practice in a safe, legal environment.

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Crafted by XESXOR Research • 2026-08-24 • PortSwigger Web Security Academy • Lab: Bypassing Referer-based CSRF defenses