Wednesday, June 15, 2011

Changing APT Tactics: Remote-Access Tools vs. Stolen Credentials

Advanced Persistent Threats (APT) are adaptive, their tactics will cycle after an intrusion takes place. For example, an APT group may start to lean away from RATs (remote-access tools) and rely more on stolen credentials. Let me explain.

An APT initially will enter the network via malware, typically through spear-phishing. Once on the compromised host, the threat actor will place one or more RATs into the environment. If we pick up RATs with our Digital DNA solution or another indicator, we start hunting them down.  After targeting and removing these RATs in the customer environment, we have found that specific malware will last about a week, maybe two, before the APT drops it altogether and switches tactics to remain in the network. We commonly see APT shift to using stolen credentials and no malware at all.

Stolen credentials are the very currency of APT. As it turns out, it’s much harder to detect malicious users than to detect RATs. In fact, the APT will use these accounts the same way a legitimate admin would – making it very hard to tell the difference. They create file shares,  use the ADMIN$ share, and defrag the hard drive. APTs will even update the AV and patch the machine. Of course, the defrag is actually a way to cover up forensic evidence on the drive, and the ADMIN$ is a way to laterally move malware and tools between machines. One would think that upgrading the AV would be counter to an APT’s self preservation. Actually, the APT updates it purely for self preservation – to appear “normal” as a legitimate admin.

At this point in the investigation, in terms of malware, we are still picking up a great deal of material – but not RATs. When the APT shifts to credentials, we start to pick up password sniffers and keyloggers that have no outside network capability. The malware in this case is entirely focused on obtaining more credentials. Finally, once the customer updates all the passwords, one or more RATs pop out of the woodwork and the cycle repeats itself.