Threat Awareness – Unpatched Microsoft Exchange Servers Infected with IIS Backdoors
Multiple security researchers have discovered that threat actors are increasingly employing malicious Internet Information Services (IIS) web server extensions to backdoor unpatched Exchange servers. These malicious IIS extensions provide adversaries with a durable persistence tool and are harder to detect than web shells with traditional security tools “since they mainly reside in the same directories as legitimate modules used by target applications,” according to Microsoft.