Exchange CVE-2020-0688: A Default Key Made Every Server Alike
On 11 February 2020, Microsoft disclosed CVE-2020-0688, a remote code execution vulnerability in Microsoft Exchange Server’s Unified Messaging service that scored 9.8 on CVSS because every installation shipped with the same cryptographic validation key by default. Any authenticated user could send a specially crafted viewstate to the Exchange Control Panel and achieve RCE as SYSTEM, and because service accounts and weak credentials were everywhere, authenticated was a low bar. This analysis walks the vulnerable request path, the viewstate forgery mechanics, the patch, and the long tail of scanning and exploitation that followed for months.
