TL;DR: 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 could have 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.
HackerOne Web Authentication Endpoint Credentials Brute-Force Vulnerability
I publicly disclosed a vulnerability that I found on and reported to the HackerOne platform. It involved a brute-force rate limiting protection bypass via IPv6. It can be found here.
InstaBrute: Two Ways to Brute-force Instagram Account Credentials
TL;DR: Instagram contained two distinct vulnerabilities that allowed an attacker to brute-force passwords of user accounts. Combined with user enumeration, a weak password policy, no 2FA nor other mitigating security controls, this could have allowed an attacker to compromise many accounts without any user interaction, including high-profile ones. Facebook fixed both issues and awarded a combined bounty of $5.000. Continue Reading