Azure B2C 0-Day: An Exploit Chain from Public Keys to Microsoft Bug Bounty

This presentation will cover a complete exploit chain in Azure B2C, starting with a discovery of cryptographic misuse and leading to full account compromise in any tenant as an unauthenticated attacker. Portions of this vulnerability have been released publicly, but several pieces were omitted to provide Microsoft time to remediate the issue and not put Azure B2C environments at unnecessary risk. New details in this talk include steps to reverse engineer and discover the crypto vulnerability along with details of a novel attack for crypto key recovery. For background, Microsoft Azure B2C is an identity and access management service for customer-facing apps. Thousands of organizations use this service, including national/state/local governments, professional societies, and commercial companies. The service is also used in the public Microsoft Security Response Center (MSRC) web portal as the main method for researchers to disclose vulnerabilities as part of Microsoft's bug bounty programs. The full exploit chain was effective against the MSRC and would have allowed an attacker to enumerate details of disclosed but not-yet-patched Microsoft zero day Vulnerabilities.