But Sophos incident response team leader Peter Mackenzie says there are behavioural anomalies present in telemetry records before an attack that, while not malicious on their own, could be early indicators of an attacker sizing up the company for a ransomware attack.
This discussion, titled Five signs you're about to be attacked, was the third in a series of five articles about ransomware issued by Sophos; iTWire covered the first article last week and the second on Monday.
Mackenzie cited the following five indicators that he said warranted a second look:
- A network scanner, especially on a server;
- Tools for disabling anti-virus software;
- The presence of Mimikatz, an open-source application that allows users to view and save authentication credentials like Kerberos tickets;
- Patterns of suspicious behaviour; and
- Test attacks.
"Attackers use legitimate admin tools to set the stage for ransomware attacks. Without knowing what tools administrators normally use on their machines, one could easily overlook this data. In hindsight, these five indicators represent investigative red flags."
He said anyone who was looking at a prospective target usually began by gaining access to one machine on the company's network where they searched for information. "[What they look for is information like] is this a Mac or Windows system, what’s the domain and company name, what kind of admin rights does the computer have, and more," Mackenzie said.
"Next, attackers will want to know what else is on the network and what can they access. The easiest way to determine this is to scan the network. If a network scanner, such as AngryIP or Advanced Port Scanner, is detected, question admin staff. If no one admits using the scanner, then it is time to investigate."
He said any indication that software used to disable anti-virus software was present on a system should be viewed with suspicion.
"Once attackers have admin rights, they will often try to disable security software using applications created to assist with the forced removal of software, such as Process Hacker, IOBit Uninstaller, GMER, and PC Hunter," Mackenzie said.
"These types of commercial tools are legitimate, but in the wrong hands, security teams and admins need to question why they have suddenly appeared."
The presence of Mimikatz was a red flag that had to be investigated, if nobody in an admin team was using it. "Any detection of Mimikatz anywhere should be investigated. If no one on an admin team can vouch for using Mimikatz, this is a red flag because it is one of the most commonly used hacking tools for credential theft," he explained.
"Attackers also use Microsoft Process Explorer, included in Windows Sysinternals, a legitimate tool that can dump LSASS.exe from memory, creating a .dmp file. They can then take this to their own environment and use Mimikatz to safely extract user names and passwords on their own test machine."
Mackenzie said another indicator of a possible future attack was when any detection took place at the same time every day, even if the malicious files found were detected and removed.
He said this was often an indication that something was going on. "Security teams should ask 'why is it coming back?' Incident responders know it normally means that something else malicious has been occurring that hasn’t (as of yet) been identified."
And, finally, he said attackers occasionally carried out small test attacks on a few machines to see if their deployment methods were working as expected and whether ransomware executed successfully or was stopped by security software on the target machines.
"If the security tools stop the attack, they [attackers] change their tactics and try again. This will show their hand, and attackers will know their time is now limited. It is often a matter of hours before a much larger attack is launched," Mackenzie said.