Stealing Money from ISPs Through Premium Rate Calls
I think the best hacks are the ones that are obvious once they’re explained, but no one has thought of them before. Here’s an example:
Instagram ($2000), Google ($0) and Microsoft ($500) were vulnerable to direct money theft via premium phone number calls. They all offer services to supply users with a token via a computer-voiced phone call, but neglected to properly verify whether supplied phone numbers were legitimate, non-premium numbers. This allowed a dedicated attacker to steal thousands of EUR/USD/GBP/… . Microsoft was exceptionally vulnerable to mass exploitation by supporting virtually unlimited concurrent calls to one premium number. The vulnerabilities were submitted to the respective Bug Bounty programs and properly resolved.