Trojan.Win32.Agent.xbfmry

Adversaries may achieve persistence by adding a program to a startup folder or referencing it with a Registry run key. Adding an entry to the “run keys” in the Registry or startup folder will cause the program referenced to be executed when a user logs in.(Citation: Microsoft Run Key) These programs will be executed under the context of the user and will have the account’s associated permissions level.

The following run keys are created by default on Windows systems:

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunOnce

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunOnce

Run keys may exist under multiple hives.(Citation: Microsoft Wow6432Node 2018)(Citation: Malwarebytes Wow6432Node 2016) The HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunOnceEx is also available but is not created by default on Windows Vista and newer. Registry run key entries can reference programs directly or list them as a dependency.(Citation: Microsoft Run Key) For example, it is possible to load a DLL at logon using a “Depend” key with RunOnceEx: reg add HKLMSOFTWAREMicrosoftWindowsCurrentVersionRunOnceEx001Depend /v 1 /d "C:tempevil[.]dll" (Citation: Oddvar Moe RunOnceEx Mar 2018)

Placing a program within a startup folder will also cause that program to execute when a user logs in. There is a startup folder location for individual user accounts as well as a system-wide startup folder that will be checked regardless of which user account logs in. The startup folder path for the current user is C:Users\[Username]AppDataRoamingMicrosoftWindowsStart MenuProgramsStartup. The startup folder path for all users is C:ProgramDataMicrosoftWindowsStart MenuProgramsStartUp.

The following Registry keys can be used to set startup folder items for persistence:

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExplorerUser Shell Folders

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExplorerShell Folders

* HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorerShell Folders

* HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorerUser Shell Folders

The following Registry keys can control automatic startup of services during boot:

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServicesOnce

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunServicesOnce

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServices

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunServices

Using policy settings to specify startup programs creates corresponding values in either of two Registry keys:

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionPoliciesExplorerRun

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionPoliciesExplorerRun

Programs listed in the load value of the registry key HKEY_CURRENT_USERSoftwareMicrosoftWindows NTCurrentVersionWindows run automatically for the currently logged-on user.

By default, the multistring BootExecute value of the registry key HKEY_LOCAL_MACHINESystemCurrentControlSetControlSession Manager is set to autocheck autochk *. This value causes Windows, at startup, to check the file-system integrity of the hard disks if the system has been shut down abnormally. Adversaries can add other programs or processes to this registry value which will automatically launch at boot.

Adversaries can use these configuration locations to execute malware, such as remote access tools, to maintain persistence through system reboots. Adversaries may also use Masquerading to make the Registry entries look as if they are associated with legitimate programs.

Adversaries may achieve persistence by adding a program to a startup folder or referencing it with a Registry run key. Adding an entry to the “run keys” in the Registry or startup folder will cause the program referenced to be executed when a user logs in.(Citation: Microsoft Run Key) These programs will be executed under the context of the user and will have the account’s associated permissions level.

The following run keys are created by default on Windows systems:

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunOnce

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunOnce

Run keys may exist under multiple hives.(Citation: Microsoft Wow6432Node 2018)(Citation: Malwarebytes Wow6432Node 2016) The HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunOnceEx is also available but is not created by default on Windows Vista and newer. Registry run key entries can reference programs directly or list them as a dependency.(Citation: Microsoft Run Key) For example, it is possible to load a DLL at logon using a “Depend” key with RunOnceEx: reg add HKLMSOFTWAREMicrosoftWindowsCurrentVersionRunOnceEx001Depend /v 1 /d "C:tempevil[.]dll" (Citation: Oddvar Moe RunOnceEx Mar 2018)

Placing a program within a startup folder will also cause that program to execute when a user logs in. There is a startup folder location for individual user accounts as well as a system-wide startup folder that will be checked regardless of which user account logs in. The startup folder path for the current user is C:Users\[Username]AppDataRoamingMicrosoftWindowsStart MenuProgramsStartup. The startup folder path for all users is C:ProgramDataMicrosoftWindowsStart MenuProgramsStartUp.

The following Registry keys can be used to set startup folder items for persistence:

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExplorerUser Shell Folders

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExplorerShell Folders

* HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorerShell Folders

* HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorerUser Shell Folders

The following Registry keys can control automatic startup of services during boot:

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServicesOnce

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunServicesOnce

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServices

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunServices

Using policy settings to specify startup programs creates corresponding values in either of two Registry keys:

* HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionPoliciesExplorerRun

* HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionPoliciesExplorerRun

Programs listed in the load value of the registry key HKEY_CURRENT_USERSoftwareMicrosoftWindows NTCurrentVersionWindows run automatically for the currently logged-on user.

By default, the multistring BootExecute value of the registry key HKEY_LOCAL_MACHINESystemCurrentControlSetControlSession Manager is set to autocheck autochk *. This value causes Windows, at startup, to check the file-system integrity of the hard disks if the system has been shut down abnormally. Adversaries can add other programs or processes to this registry value which will automatically launch at boot.

Adversaries can use these configuration locations to execute malware, such as remote access tools, to maintain persistence through system reboots. Adversaries may also use Masquerading to make the Registry entries look as if they are associated with legitimate programs.

Adversaries may interact with the Windows Registry to hide configuration information within Registry keys, remove information as part of cleaning up, or as part of other techniques to aid in persistence and execution.

Access to specific areas of the Registry depends on account permissions, some requiring administrator-level access. The built-in Windows command-line utility Reg may be used for local or remote Registry modification. (Citation: Microsoft Reg) Other tools may also be used, such as a remote access tool, which may contain functionality to interact with the Registry through the Windows API.

Registry modifications may also include actions to hide keys, such as prepending key names with a null character, which will cause an error and/or be ignored when read via Reg or other utilities using the Win32 API. (Citation: Microsoft Reghide NOV 2006) Adversaries may abuse these pseudo-hidden keys to conceal payloads/commands used to maintain persistence. (Citation: TrendMicro POWELIKS AUG 2014) (Citation: SpectorOps Hiding Reg Jul 2017)

The Registry of a remote system may be modified to aid in execution of files as part of lateral movement. It requires the remote Registry service to be running on the target system. (Citation: Microsoft Remote) Often Valid Accounts are required, along with access to the remote system’s SMB/Windows Admin Shares for RPC communication.

Adversaries may employ various system checks to detect and avoid virtualization and analysis environments. This may include changing behaviors based on the results of checks for the presence of artifacts indicative of a virtual machine environment (VME) or sandbox. If the adversary detects a VME, they may alter their malware to disengage from the victim or conceal the core functions of the implant. They may also search for VME artifacts before dropping secondary or additional payloads. Adversaries may use the information learned from Virtualization/Sandbox Evasion during automated discovery to shape follow-on behaviors.(Citation: Deloitte Environment Awareness)

Specific checks will vary based on the target and/or adversary, but may involve behaviors such as Windows Management Instrumentation, PowerShell, System Information Discovery, and Query Registry to obtain system information and search for VME artifacts. Adversaries may search for VME artifacts in memory, processes, file system, hardware, and/or the Registry. Adversaries may use scripting to automate these checks into one script and then have the program exit if it determines the system to be a virtual environment.

Checks could include generic system properties such as host/domain name and samples of network traffic. Adversaries may also check the network adapters addresses, CPU core count, and available memory/drive size.

Other common checks may enumerate services running that are unique to these applications, installed programs on the system, manufacturer/product fields for strings relating to virtual machine applications, and VME-specific hardware/processor instructions.(Citation: McAfee Virtual Jan 2017) In applications like VMWare, adversaries can also use a special I/O port to send commands and receive output.

Hardware checks, such as the presence of the fan, temperature, and audio devices, could also be used to gather evidence that can be indicative a virtual environment. Adversaries may also query for specific readings from these devices.(Citation: Unit 42 OilRig Sept 2018)

Adversaries may set files and directories to be hidden to evade detection mechanisms. To prevent normal users from accidentally changing special files on a system, most operating systems have the concept of a ‘hidden’ file. These files don’t show up when a user browses the file system with a GUI or when using normal commands on the command line. Users must explicitly ask to show the hidden files either via a series of Graphical User Interface (GUI) prompts or with command line switches (dir /a for Windows and ls –a for Linux and macOS).

On Linux and Mac, users can mark specific files as hidden simply by putting a “.” as the first character in the file or folder name (Citation: Sofacy Komplex Trojan) (Citation: Antiquated Mac Malware). Files and folders that start with a period, ‘.’, are by default hidden from being viewed in the Finder application and standard command-line utilities like “ls”. Users must specifically change settings to have these files viewable.

Files on macOS can also be marked with the UF_HIDDEN flag which prevents them from being seen in Finder.app, but still allows them to be seen in Terminal.app (Citation: WireLurker). On Windows, users can mark specific files as hidden by using the attrib.exe binary. Many applications create these hidden files and folders to store information so that it doesn’t clutter up the user’s workspace. For example, SSH utilities create a .ssh folder that’s hidden and contains the user’s known hosts and keys.

Adversaries can use this to their advantage to hide files and folders anywhere on the system and evading a typical user or system analysis that does not incorporate investigation of hidden files.

Adversaries may acquire credentials from web browsers by reading files specific to the target browser.(Citation: Talos Olympic Destroyer 2018) Web browsers commonly save credentials such as website usernames and passwords so that they do not need to be entered manually in the future. Web browsers typically store the credentials in an encrypted format within a credential store; however, methods exist to extract plaintext credentials from web browsers.

For example, on Windows systems, encrypted credentials may be obtained from Google Chrome by reading a database file, AppDataLocalGoogleChromeUser DataDefaultLogin Data and executing a SQL query: SELECT action_url, username_value, password_value FROM logins;. The plaintext password can then be obtained by passing the encrypted credentials to the Windows API function CryptUnprotectData, which uses the victim’s cached logon credentials as the decryption key.(Citation: Microsoft CryptUnprotectData April 2018)

Adversaries have executed similar procedures for common web browsers such as FireFox, Safari, Edge, etc.(Citation: Proofpoint Vega Credential Stealer May 2018)(Citation: FireEye HawkEye Malware July 2017) Windows stores Internet Explorer and Microsoft Edge credentials in Credential Lockers managed by the Windows Credential Manager.

Adversaries may also acquire credentials by searching web browser process memory for patterns that commonly match credentials.(Citation: GitHub Mimikittenz July 2016)

After acquiring credentials from web browsers, adversaries may attempt to recycle the credentials across different systems and/or accounts in order to expand access. This can result in significantly furthering an adversary’s objective in cases where credentials gained from web browsers overlap with privileged accounts (e.g. domain administrator).

Adversaries may employ various system checks to detect and avoid virtualization and analysis environments. This may include changing behaviors based on the results of checks for the presence of artifacts indicative of a virtual machine environment (VME) or sandbox. If the adversary detects a VME, they may alter their malware to disengage from the victim or conceal the core functions of the implant. They may also search for VME artifacts before dropping secondary or additional payloads. Adversaries may use the information learned from Virtualization/Sandbox Evasion during automated discovery to shape follow-on behaviors.(Citation: Deloitte Environment Awareness)

Specific checks will vary based on the target and/or adversary, but may involve behaviors such as Windows Management Instrumentation, PowerShell, System Information Discovery, and Query Registry to obtain system information and search for VME artifacts. Adversaries may search for VME artifacts in memory, processes, file system, hardware, and/or the Registry. Adversaries may use scripting to automate these checks into one script and then have the program exit if it determines the system to be a virtual environment.

Checks could include generic system properties such as host/domain name and samples of network traffic. Adversaries may also check the network adapters addresses, CPU core count, and available memory/drive size.

Other common checks may enumerate services running that are unique to these applications, installed programs on the system, manufacturer/product fields for strings relating to virtual machine applications, and VME-specific hardware/processor instructions.(Citation: McAfee Virtual Jan 2017) In applications like VMWare, adversaries can also use a special I/O port to send commands and receive output.

Hardware checks, such as the presence of the fan, temperature, and audio devices, could also be used to gather evidence that can be indicative a virtual environment. Adversaries may also query for specific readings from these devices.(Citation: Unit 42 OilRig Sept 2018)