Track Common Adversary Tasks Performed Using AutoIt backdoor

Adversaries may abuse PowerShell commands and scripts for execution. PowerShell is a powerful interactive command-line interface and scripting environment included in the Windows operating system. Adversaries can use PowerShell to perform a number of actions, including discovery of information and execution of code. Examples include the Start-Process cmdlet which can be used to run an executable and the Invoke-Command cmdlet which runs a command locally or on a remote computer (though administrator permissions are required to use PowerShell to connect to remote systems).

PowerShell may also be used to download and run executables from the Internet, which can be executed from disk or in memory without touching disk.

A number of PowerShell-based offensive testing tools are available, including Empire, PowerSploit, PoshC2, and PSAttack.

PowerShell commands/scripts can also be executed without directly invoking the powershell.exe binary through interfaces to PowerShell's underlying System.Management.Automation assembly DLL exposed through the .NET framework and Windows Common Language Interface (CLI).

Antivirus/Antimalware

Anti-virus can be used to automatically quarantine suspicious files.

Code Signing

Set PowerShell execution policy to execute only signed scripts.

Disable or Remove Feature or Program

It may be possible to remove PowerShell from systems when not needed, but a review should be performed to assess the impact to an environment, since it could be in use for many legitimate purposes and administrative functions.

Disable/restrict the WinRM Service to help prevent uses of PowerShell for remote execution.

Execution Prevention

Use application control where appropriate.

Privileged Account Management

When PowerShell is necessary, restrict PowerShell execution policy to administrators. Be aware that there are methods of bypassing the PowerShell execution policy, depending on environment configuration.

Monitoring the following activities in your Organization can help you detect this technique.

Command: Command Execution

Invoking a computer program directive to perform a specific task (ex: Windows EID 4688 of cmd.exe showing command-line parameters, ~/.bash_history, or ~/.zsh_history)

If proper execution policy is set, adversaries will likely be able to define their own execution policy if they obtain administrator or system access, either through the Registry or at the command line. This change in policy on a system may be a way to detect malicious use of PowerShell. If PowerShell is not used in an environment, then simply looking for PowerShell execution may detect malicious activity. It is also beneficial to turn on PowerShell logging to gain increased fidelity in what occurs during execution (which is applied to .NET invocations).  PowerShell 5.0 introduced enhanced logging capabilities, and some of those features have since been added to PowerShell 4.0. Earlier versions of PowerShell do not have many logging features. An organization can gather PowerShell execution details in a data analytic platform to supplement it with other data.

Module: Module Load

Attaching a module into the memory of a process/program, typically to access shared resources/features provided by the module (ex: Sysmon EID 7)

Monitor for loading and/or execution of artifacts associated with PowerShell specific assemblies, such as System.Management.Automation.dll (especially to unusual process names/locations).

Process: Process Creation

Birth of a new running process (ex: Sysmon EID 1 or Windows EID 4688)

Monitor for newly executed processes that may abuse PowerShell commands and scripts for execution.

Process: Process Metadata

Contextual data about a running process, which may include information such as environment variables, image name, user/owner, etc.

Consider monitoring for Windows event ID (EID) 400, which shows the version of PowerShell executing in the EngineVersion field (which may also be relevant to detecting a potential Downgrade Attack) as well as if PowerShell is running locally or remotely in the HostName field. Furthermore, EID 400 may indicate the start time and EID 403 indicates the end time of a PowerShell session.

Script: Script Execution

Launching a list of commands through a script file (ex: Windows EID 4104)

Monitor for any attempts to enable scripts running on a system would be considered suspicious. If scripts are not commonly used on a system, but enabled, scripts running out of cycle from patching or other administrator functions are suspicious. Scripts should be captured from the file system when possible to determine their actions and intent.

Adversaries may bypass UAC mechanisms to elevate process privileges on system. Windows User Account Control (UAC) allows a program to elevate its privileges (tracked as integrity levels ranging from low to high) to perform a task under administrator-level permissions, possibly by prompting the user for confirmation. The impact to the user ranges from denying the operation under high enforcement to allowing the user to perform the action if they are in the local administrators group and click through the prompt or allowing them to enter an administrator password to complete the action.

If the UAC protection level of a computer is set to anything but the highest level, certain Windows programs can elevate privileges or execute some elevated Component Object Model objects without prompting the user through the UAC notification box. An example of this is use of Rundll32 to load a specifically crafted DLL which loads an auto-elevated Component Object Model object and performs a file operation in a protected directory which would typically require elevated access. Malicious software may also be injected into a trusted process to gain elevated privileges without prompting a user.

Many methods have been discovered to bypass UAC. The Github readme page for UACME contains an extensive list of methods that have been discovered and implemented, but may not be a comprehensive list of bypasses. Additional bypass methods are regularly discovered and some used in the wild, such as:

• eventvwr.exe can auto-elevate and execute a specified binary or script.

Another bypass is possible through some lateral movement techniques if credentials for an account with administrator privileges are known, since UAC is a single system security mechanism, and the privilege or integrity of a process running on one system will be unknown on remote systems and default to high integrity.

Audit

Check for common UAC bypass weaknesses on Windows systems to be aware of the risk posture and address issues where appropriate.

Privileged Account Management

Remove users from the local administrator group on systems.

Update Software

Consider updating Windows to the latest version and patch level to utilize the latest protective measures against UAC bypass.

User Account Control

Although UAC bypass techniques exist, it is still prudent to use the highest enforcement level for UAC when possible and mitigate bypass opportunities that exist with techniques such as DLL Search Order Hijacking.

Monitoring the following activities in your Organization can help you detect this technique.

Command: Command Execution

Invoking a computer program directive to perform a specific task (ex: Windows EID 4688 of cmd.exe showing command-line parameters, ~/.bash_history, or ~/.zsh_history)

Monitor executed commands and arguments that may bypass UAC mechanisms to elevate process privileges on system.

Process: Process Creation

Birth of a new running process (ex: Sysmon EID 1 or Windows EID 4688)

Monitor newly executed processes, such as eventvwr.exe and sdclt.exe, that may bypass UAC mechanisms to elevate process privileges on system.

Process: Process Metadata

Contextual data about a running process, which may include information such as environment variables, image name, user/owner, etc.

Monitor contextual data about a running process, which may include information such as environment variables, image name, user/owner that may bypass UAC mechanisms to elevate process privileges on system.

Windows Registry: Windows Registry Key Modification

Changes made to a Registry Key and/or Key value (ex: Windows EID 4657 or Sysmon EID 13|14)

Some UAC bypass methods rely on modifying specific, user-accessible Registry settings. For example:* The eventvwr.exe bypass uses the [HKEY_CURRENT_USER]\Software\Classes\mscfile\shell\open\command Registry key. * The sdclt.exe bypass uses the [HKEY_CURRENT_USER]\Software\Microsoft\Windows\CurrentVersion\App Paths\control.exe and [HKEY_CURRENT_USER]\Software\Classes\exefile\shell\runas\command\isolatedCommand Registry keys. Analysts should monitor these Registry settings for unauthorized changes.

Adversaries may encode data with a standard data encoding system to make the content of command and control traffic more difficult to detect. Command and control (C2) information can be encoded using a standard data encoding system that adheres to existing protocol specifications. Common data encoding schemes include ASCII, Unicode, hexadecimal, Base64, and MIME. Some data encoding systems may also result in data compression, such as gzip.

Network Intrusion Prevention

Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level. Signatures are often for unique indicators within protocols and may be based on the specific obfuscation technique used by a particular adversary or tool, and will likely be different across various malware families and versions. Adversaries will likely change tool C2 signatures over time or construct protocols in such a way as to avoid detection by common defensive tools.

Monitoring the following activities in your Organization can help you detect this technique.

Network Traffic: Network Traffic Content

Logged network traffic data showing both protocol header and body values (ex: PCAP)

Monitor for network data for uncommon data flows (e.g., a client sending significantly more data than it receives from a server). Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. Analyze packet contents to detect communications that do not follow the expected protocol behavior for the port that is being used.