If at some point you find a web page that presents you sensitive information based on your session: Maybe it's reflecting cookies, or printing or CC details or any other sensitive information, you may try to steal it. Here I present you the main ways to can try to achieve it:
CORS bypass: If you can bypass CORS headers you will be able to steal the information performing Ajax request for a malicious page.
XSS: If you find a XSS vulnerability on the page you may be able to abuse it to steal the information.
Danging Markup: If you cannot inject XSS tags you still may be able to steal the info using other regular HTML tags.