The next stage of the Quarantine series.
I noticed that our session cookie was a JWT, signed with HS256.
A vulnerability exists where these tokens can have their signing algorithm set to 'none' and their signature removed, and the web app will accept and process it.
I used the highly useful jwt_tool to resign it, editing my 'privilege' value from '1' to '10'.
This allowed me access to the admin panel (more of a single page).