Masquerading occurs when the name or location of an executable, legitimate or malicious, is manipulated or abused for the sake of evading defenses and observation. Several different variations of this technique have been observed.
One variant is for an executable to be placed in a commonly trusted directory or given the name of a legitimate, trusted program. Alternatively, the filename given may be a close approximation of legitimate programs or something innocuous. An example of this is when a common system utility or program is moved and renamed to avoid detection based on its usage. This is done to bypass tools that trust executables by relying on file name or path, as well as to deceive defenders and system administrators into thinking a file is benign by associating the name with something that is thought to be legitimate.
A third variant uses the right-to-left override (RTLO or RLO) character (U+202E) as a means of tricking a user into executing what they think is a benign file type but is actually executable code. RTLO is a non-printing character that causes the text that follows it to be displayed in reverse. For example, a Windows screensaver file named
March 25 \u202Excod.scr will display as
photo_high_re\u202Egnp.js will be displayed as
photo_high_resj.png. A common use of this technique is with spearphishing attachments since it can trick both end users and defenders if they are not aware of how their tools display and render the RTLO character. Use of the RTLO character has been seen in many targeted intrusion attempts and criminal activity. RTLO can be used in the Windows Registry as well, where regedit.exe displays the reversed characters but the command line tool reg.exe does not by default.
Adversaries may modify a binary's metadata, including such fields as icons, version, name of the product, description, and copyright, to better blend in with the environment and increase chances of deceiving a security analyst or product.
In another variation of this technique, an adversary may use a renamed copy of a legitimate utility, such as rundll32.exe.  An alternative case occurs when a legitimate utility is moved to a different directory and also renamed to avoid detections based on system utilities executing from non-standard paths. 
An example of abuse of trusted locations in Windows would be the
C:\Windows\System32 directory. Examples of trusted binary names that can be given to malicious binares include "explorer.exe" and "svchost.exe".
Another variation of this technique includes malicious binaries changing the name of their running process to that of a trusted or benign process, after they have been launched as opposed to before. 
admin@338 actors used the following command to rename one of their tools to a benign file name:
|APT1||The file name AcroRD32.exe, a legitimate process name for Adobe's Acrobat Reader, was used by APT1 as a name for malware.  |
|APT32||APT32 has used hidden or non-printing characters to help masquerade file names on a system, such as appending a Unicode no-break space character to a legitimate service name. They have also used by moving and renaming pubprn.vbs to a .txt file to avoid detection. Additionally, the group has renamed a NetCat binary to kb-10233.exe to masquerade as a Windows update.   |
|APT41||APT41 attempted to masquerade their files as popular anti-virus software. |
|BADNEWS||BADNEWS attempts to hide its payloads using legitimate filenames. |
|BRONZE BUTLER||BRONZE BUTLER has given malware the same name as an existing file on the file share server to cause users to unwittingly launch and install the malware on additional systems. |
|Calisto||Calisto's installation file is an unsigned DMG image under the guise of Intego’s security solution for mac. |
|Carbanak||Carbanak malware names itself "svchost.exe," which is the name of the Windows shared service host program. |
|Catchamas||Catchamas adds a new service named NetAdapter in an apparent attempt to masquerade as a legitimate service. |
|ChChes||ChChes copies itself to an .exe file with a filename that is likely intended to imitate Norton Antivirus but has several letters reversed (e.g. notron.exe). |
|CozyCar||The CozyCar dropper has masqueraded a copy of the infected system's rundll32.exe executable that was moved to the malware's install directory and renamed according to a predefined configuration file. |
|DarkComet||DarkComet has dropped itself onto victim machines with file names such as WinDefender.Exe and winupdate.exe in an apparent attempt to masquerade as legitimate. |
|Daserf||Daserf uses file and folder names related to legitimate programs in order to blend in, such as HP, Intel, Adobe, and perflogs. |
|Dragonfly 2.0||Dragonfly 2.0 created accounts disguised as legitimate backup and service accounts as well as an email administration account.  |
|Elise||If installing itself as a service fails, Elise instead writes itself as a file named svchost.exe saved in %APPDATA%\Microsoft\Network. |
|Exaramel for Windows||The Exaramel for Windows dropper creates and starts a Windows service named wsmprovav with the description “Windows Check AV” in an apparent attempt to masquerade as a legitimate service. |
|Felismus||Felismus has masqueraded as legitimate Adobe Content Management System files. |
|FIN6||FIN6 has renamed the "psexec" service name to "mstdc" to masquerade as a legitimate Windows executable. |
|FIN7||FIN7 has created a scheduled task named “AdobeFlashSync” to establish persistence. |
|FinFisher||FinFisher renames one of its .dll files to uxtheme.dll in an apparent attempt to masquerade as a legitimate file.  |
|Fysbis||Fysbis has masqueraded as trusted software rsyncd and dbus-inotifier. |
|HTTPBrowser||HTTPBrowser's installer contains a malicious file named navlu.dll to decrypt and run the RAT. navlu.dll is also the name of a legitimate Symantec DLL. |
|InnaputRAT||InnaputRAT variants have attempted to appear legitimate by using the file names SafeApp.exe and NeutralApp.exe, as well as by adding a new service named OfficeUpdateService. |
|InvisiMole||InvisiMole saves one of its files as mpr.dll in the Windows folder, masquerading as a legitimate library file. |
|Ixeshe||Ixeshe has used registry values and file names associated with Adobe software, such as AcroRd32.exe. |
|Ke3chang||Ke3chang has used the right-to-left override character in spearphishing attachment names to trick targets into executing .scr and .exe files. |
|KONNI||KONNI creates a shortcut called "Anti virus service.lnk" in an apparent attempt to masquerade as a legitimate file. |
|Kwampirs||Kwampirs establishes persistence by adding a new service with the display name "WMI Performance Adapter Extension" in an attempt to masquerade as a legitimate WMI service. |
LightNeuron has used filenames associated with Exchange and Outlook for binary and configuration files, such as
|Machete||Machete renamed payloads and task names to masquerade as legitimate Google Chrome, Java, Dropbox, Adobe Reader and Python executables. |
|menuPass||menuPass has been seen changing malicious files to appear legitimate. They have also renamed certutil and move it to a different location on system to avoid detection based on use of the tool. The group has also used esentutl to change file extensions to avoid detection.   |
|Mis-Type||Mis-Type saves itself as a file named msdtc.exe, which is also the name of the legitimate Microsoft Distributed Transaction Coordinator service.  |
|Misdat||Misdat saves itself as a file named msdtc.exe, which is also the name of the legitimate Microsoft Distributed Transaction Coordinator service.  |
|Nidiran||Nidiran can create a new service named msamger (Microsoft Security Accounts Manager), which mimics the legitimate Microsoft database by the same name.  |
|NOKKI||NOKKI is written to %LOCALAPPDATA%\MicroSoft Updatea\svServiceUpdate.exe prior being executed in a new process in an apparent attempt to masquerade as a legitimate folder and file. |
|NotPetya||NotPetya drops PsExec with the filename dllhost.dat. |
OLDBAIT installs itself in
|OSX/Shlayer||OSX/Shlayer can masquerade as a Flash Player update.  |
OwaAuth uses the filename owaauth.dll, which is a legitimate file that normally resides in
|Patchwork||Patchwork installed its payload in the startup programs folder as "Baidu Software Update." The group also adds its second stage payload to the startup programs as “Net Monitor." |
|PLATINUM||PLATINUM has renamed rar.exe to avoid detection. |
|PlugX||In one instance, menuPass added PlugX as a service with a display name of "Corel Writing Tools Utility." |
|Poseidon Group||Poseidon Group tools attempt to spoof anti-virus processes as a means of self-defense. |
|POWERSTATS||POWERSTATS has created a scheduled task named "MicrosoftEdge" to establish persistence. |
|PUNCHBUGGY||PUNCHBUGGY mimics filenames from %SYSTEM%\System32 to hide DLLs in %WINDIR% and/or %TEMP%.  |
QUADAGENT used the PowerShell filenames
|QuasarRAT||QuasarRAT has dropped binaries as files named microsoft_network.exe and crome.exe. |
|RawPOS||New services created by RawPOS are made to appear like legitimate Windows services, with names such as "Windows Management Help Service", "Microsoft Support", and "Windows Advanced Task Manager".   |
|Remsec||The Remsec loader implements itself with the name Security Support Provider, a legitimate Windows function. Various Remsec .exe files mimic legitimate file names used by Microsoft, Symantec, Kaspersky, Hewlett-Packard, and VMWare. Remsec also disguised malicious modules using similar filenames as custom network encryption software on victims.  |
|S-Type||S-Type may save itself as a file named msdtc.exe, which is also the name of the legitimate Microsoft Distributed Transaction Coordinator service.  |
|Scarlet Mimic||Scarlet Mimic has used the left-to-right override character in self-extracting RAR archive spearphishing attachment file names. |
|Seasalt||Seasalt has masqueraded as a service called "SaSaut" with a display name of "System Authorization Service" in an apparent attempt to masquerade as a legitimate service. |
|Shamoon||Shamoon creates a new service named “ntssrv” that attempts to appear legitimate; the service's display name is “Microsoft Network Realtime Inspection Service” and its description is “Helps guard against time change attempts targeting known and newly discovered vulnerabilities in network time protocols.” |
|Soft Cell||Soft Cell used a renamed cmd.exe file to evade detection. |
Sowbug named its tools to masquerade as Windows or Adobe Reader software, such as by using the file name adobecms.exe and the directory
|SslMM||To establish persistence, SslMM identifies the Start Menu Startup directory and drops a link to its own executable disguised as an “Office Start,” “Yahoo Talk,” “MSN Gaming Z0ne,” or “MSN Talk” shortcut. |
|Starloader||Starloader has masqueraded as legitimate software update packages such as Adobe Acrobat Reader and Intel. |
|TEMP.Veles||TEMP.Veles has performed a variety of methods to look like valid users, including renaming files and mimicking legitimate administrator activities. |
|Truvasys||To establish persistence, Truvasys adds a Registry Run key with a value "TaskMgr" in an attempt to masquerade as the legitimate Windows Task Manager. |
|Ursnif||Ursnif has used strings from legitimate system files and existing folders for its file, folder, and Registry entry names. |
|USBStealer||USBStealer mimics a legitimate Russian program called USB Disk Security. |
|Volgmer||Some Volgmer variants add new services with display names generated by a list of hard-coded strings such as Application, Background, Security, and Windows, presumably as a way to masquerade as a legitimate service.  |
|Winnti||A Winnti implant file was named ASPNET_FILTER.DLL, mimicking the legitimate ASP.NET ISAPI filter DLL with the same name. |
|yty||yty contains several references to football (including "football," "score," "ball," and "loose") in a likely attempt to disguise its traffic. |
|ZLib||ZLib mimics the resource version information of legitimate Realtek Semiconductor, Nvidia, or Synaptics modules. |
|Code Signing||Require signed binaries.|
|Execution Prevention||Use tools that restrict program execution via whitelisting by attributes other than file name for common operating system utilities that are needed.|
|Restrict File and Directory Permissions||Use file system access controls to protect folders such as C:\Windows\System32.|
Collect file hashes; file names that do not match their expected hash are suspect. Perform file monitoring; files with known names but in unusual locations are suspect. Likewise, files that are modified outside of an update or patch are suspect.
If file names are mismatched between the file name on disk and that of the binary's PE metadata, this is a likely indicator that a binary was renamed after it was compiled. Collecting and comparing disk and resource filenames for binaries by looking to see if the InternalName, OriginalFilename, and/or ProductName match what is expected could provide useful leads, but may not always be indicative of malicious activity.  Do not focus on the possible names a file could have, but instead on the command-line arguments that are known to be used and are distinct because it will have a better rate of detection.
For RTLO, detection methods should include looking for common formats of RTLO characters within filenames such as "\u202E", "[U+202E]", and "%E2%80%AE". Defenders should also check their analysis tools to ensure they do not interpret the RTLO character and instead print the true name of the a file containing it.
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