This tip highlights a technique to bypass web application firewalls (WAFs) or IP restriction functions by manipulating how IP addresses are represented in HTTP headers. The method involves setting an IP address value such as 1.1.1.1 in the application and then brute forcing various HTTP headers using the same IP address value. The idea is to find a header that the application or WAF uses to determine the client's IP and that can be manipulated to bypass IP-based access controls.
Many applications and WAFs rely on HTTP headers like X-Forwarded-For, X-Real-IP, or other custom headers to identify the client's IP address. By trying different headers with the same IP value, an attacker might find a way to trick the system into allowing access when it should be denied. This kind of bypass affects any system relying on IP restriction mechanisms that can be influenced by HTTP header values.
The user in the tweet provided a wordlist for brute forcing headers, which can be used to automate testing multiple potential headers to find one that can bypass the IP restriction. This approach is universal since it doesn't depend on a specific vulnerability like XSS or SQLi but targets access controls based on IPs present in HTTP headers.
In essence, security testers and bug bounty hunters should consider testing IP restriction by brute forcing different headers with the same IP value to identify potential bypasses. Developers and security teams should ensure they validate the client's IP address reliably and do not trust user-controllable headers without proper checks.
For more insights, check out the original tweet here: https://twitter.com/0xbartita/status/1937236149279342773