Your best defense against ransomware: Find the early warning signs

This post was originally published on this site

As ransomware continues to prove how devastating it can be, one of the scariest things for security pros is how quickly it can paralyze an organization. Just look at Honda, which was forced to shut down all global operations in June, and Garmin, which had its services knocked offline for days in July.

Ransomware isn’t hard to detect but identifying it when the encryption and exfiltration are rampant is too little too late. However, there are several warning signs that organizations can catch before the real damage is done. In fact, FireEye found that there is usually three days of dwell time between these early warning signs and detonation of ransomware.

So, how does a security team find these weak but important early warning signals? Somewhat surprisingly perhaps, the network provides a unique vantage point to spot the pre-encryption activity of ransomware actors such as those behind Maze.

Here’s a guide, broken down by MITRE category, of the many different warning signs organizations being attacked by Maze ransomware can see and act upon before it’s too late.

Initial access

With Maze actors, there are several initial access vectors, such as phishing attachments and links, external-facing remote access such as Microsoft’s Remote Desktop Protocol (RDP), and access via valid accounts. All of these can be discovered while network threat hunting across traffic. Furthermore, given this represents the actor’s earliest foray into the environment, detecting this initial access is the organization’s best bet to significantly mitigate impact.

ATT&CK techniques

Hunt for…

T1193 Spear-phishing attachment
T1192 Spear-phishing link

  • Previously unseen or newly registered domains, unique registrars
  • Doppelgangers of your organization / partner’s domains or Alexa top 500
T133 External Remote Services
  • Inbound RDP from external devices
T1078 Valid accounts
  • Exposed passwords across SMB, FTP, HTTP, and other clear text usage
T1190 Exploit public-facing application
  • Exposure and exploit to known vulnerabilities

Execution

The execution phase is still early enough in an attack to shut it down and foil any attempts to detonate ransomware. Common early warning signs to watch for in execution include users being tricked into clicking a phishing link or attachment, or when certain tools such as PsExec have been used in the environment.

ATT&CK techniques

Hunt for…

T1024 User execution

  • Suspicious email behaviors from users and associated downloads
T1035 Service execution
  • File IO over SMB using PsExec, extracting contents on one system and then later on another system
T1028 Windows remote management
  • Remote management connections excluding known good devices

Persistence

Adversaries using Maze rely on several common techniques, such as a web shell on internet-facing systems and the use of valid accounts obtained within the environment. Once the adversary has secured a foothold, it starts to become increasingly difficult to mitigate impact.

ATT&CK techniques

Hunt for…

T1100 Web shell

  • Unique activity connections (e.g. atypical ports and user agents) from external connections
T1078 Valid accounts
  • Remote copy of KeePass file stores across SMB or HTTP

Privilege escalation

As an adversary gains higher levels of access it becomes significantly more difficult to pick up additional signs of activity in the environment. For the actors of Maze, the techniques used for persistence are similar to those for privileged activity.

ATT&CK techniques

Hunt for…

T1100 Web shell

  • Web shells on external facing web and gateway systems
T1078 Valid accounts
  • Remote copy of password files across SMB (e.g. files with “passw”)

Defense evasion

To hide files and their access to different systems, adversaries like the ones who use Maze will rename files, encode, archive, and use other mechanisms to hide their tracks. Attempts to hide their traces are in themselves indicators to hunt for.

ATT&CK techniques

Hunt for…

T1027 Obfuscated files or information

  • Adversary tools by port usage, certificate issuer name, or unknown protocol communications
T1078 Valid accounts
  • New account creation from workstations and other non-admin used devices

Credential access

There are several defensive controls that can be put in place to help limit or restrict access to credentials. Threat hunters can enable this process by providing situational awareness of network hygiene including specific attack tool usage, credential misuse attempts and weak or insecure passwords.

ATT&CK techniques

Hunt for…

T110 Brute force

  • RDP brute force attempts against known username accounts
T1081 Credentials in files
  • Unencrypted passwords and password files in the environment

Discovery

Maze adversaries use a number of different methods for internal reconnaissance and discovery. For example, enumeration and data collection tools and methods leave their own trail of evidence that can be identified before the exfiltration and encryption occurs.

ATT&CK techniques

Hunt for…

T1201 Password policy discovery

  • Traffic of devices copying the password policy off file shares
  • Enumeration of password policy
T1018 Remote system discovery

T1087 Account discovery

T1016 System network configuration discovery

T1135 Network share discovery

T1083 File and directory discovery

  • Enumeration for computer names, accounts, network connections, network configurations, or files

Lateral movement

Ransomware actors use lateral movement to understand the environment, spread through the network and then to collect and prepare data for encryption / exfiltration.

ATT&CK techniques

Hunt for…

T1105 Remote file copy

T1077 Windows admin shares

  • Suspicious SMB file write activity
  • PsExec usage to copy attack tools or access other systems
  • Attack tools copied across SMB
T1076 Remote Desktop Protocol

T1028 Windows remote management

T1097 Pass the ticket

  • HTTP POST with the use of WinRM user agent
  • Enumeration of remote management capabilities
  • Non-admin devices with RDP activity

Collection

In this phase, Maze actors use tools and batch scripts to collect information and prepare for exfiltration. It is typical to find .bat files or archives using the .7z or .exe extension at this stage.

ATT&CK techniques

Hunt for…

T1039 Data from network share drive

  • Suspicious or uncommon remote system data collection activity

Command and control (C2)

Many adversaries will use common ports or remote access tools to try and obtain and maintain C2, and Maze actors are no different. In the research my team has done, we’ve also seen the use of ICMP tunnels to connect to the attacker infrastructure.

ATT&CK techniques

Hunt for…

T1043 Common used port

T1071 Standard application layer protocol

  • ICMP callouts to IP addresses
  • Non-browser originating HTTP traffic
  • Unique device HTTP script like requests
T1105 Remote file copy
  • Downloads of remote access tools through string searches
T1219 Remote access tools
  • Cobalt strike BEACON and FTP to directories with cobalt in the name

Exfiltration

At this stage, the risk of exposure of sensitive data in the public realm is dire and it means an organization has missed many of the earlier warning signs—now it’s about minimizing impact.

ATT&CK techniques

Hunt for…

T1030 Data transfer size limits

  • External device traffic to uncommon destinations
T1048 Exfiltration over alternative protocol
  • Unknown FTP outbound
T1002: Data compressed
  • Archive file extraction

Summary

Ransomware is never good news when it shows up at the doorstep. However, with disciplined network threat hunting and monitoring, it is possible to identify an attack early in the lifecycle. Many of the early warning signs are visible on the network and threat hunters would be well served to identify these and thus help mitigate impact.

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September 23, 2020