A custom injection point in SQLmap allows you to specify exactly where and how SQLmap should attempt to inject payloads into a request. This is useful when dealing with more complex or non-standard injection scenarios that SQLmap may not detect automatically. By defining a custom injection point with the wildcard character '`*`' , you have finer control over the testing process, ensuring SQLmap targets specific parts of the request you suspect to be vulnerable.
sqlmap -u "http://example.com" --data "username=admin&password=pass" --headers="x-forwarded-for:127.0.0.1*"Source: SQL Injection/SQLmap.md in PayloadsAllTheThings. From PayloadsAllTheThings by Swissky and contributors. MIT License, Copyright (c) 2019 Swissky.