hackerone vulnerability: how to use XSSI to steal a multi-line string-vulnerability warning-the black bar safety net

First of all, I assume that students already know what isXSSI. If you don't know the words, you can have a look below this paragraph is taken from the identity-based XXSI attack on the simple introduction： Cross-site scripting: XSSI - Cross Site Script Inclusion is a way to allow an attacker to...