Obfuscated Files or Information

From enterprise
Jump to: navigation, search
Obfuscated Files or Information
ID T1027
Tactic Defense Evasion
Platform Linux, Windows, macOS
Data Sources Network protocol analysis, Process use of network, Binary file metadata, File monitoring, Malware reverse engineering, Process command-line parameters, Environment variable, Process Monitoring, Windows event logs, Network intrusion detection system, Email gateway, SSL/TLS inspection
Defense Bypassed Host forensic analysis, Signature-based detection, Host intrusion prevention systems, Application whitelisting, Process whitelisting, Log analysis, Whitelisting by file name or path
Contributors Red Canary, Christiaan Beek, @ChristiaanBeek

Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit. This is common behavior that can be used across different platforms and the network to evade defenses.

Payloads may be compressed, archived, or encrypted in order to avoid detection. These payloads may be used during Initial Access or later to mitigate detection. Sometimes a user's action may be required to open and Deobfuscate/Decode Files or Information for User Execution. The user may also be required to input a password to open a password protected compressed/encrypted file that was provided by the adversary.1 Adversaries may also used compressed or archived scripts, such as Javascript.

Portions of files can also be encoded to hide the plain-text strings that would otherwise help defenders with discovery.2 Payloads may also be split into separate, seemingly benign files that only reveal malicious functionality when reassembled.3

Adversaries may also obfuscate commands executed from payloads or directly via a Command-Line Interface. Environment variables, aliases, characters, and other platform/language specific semantics can be used to evade signature based detections and whitelisting mechanisms.456

Another example of obfuscation is through the use of steganography, a technique of hiding messages or code in images, audio tracks, video clips, or text files. One of the first known and reported adversaries that used steganography activity surrounding Invoke-PSImage. The Duqu malware encrypted the gathered information from a victim's system and hid it into an image followed by exfiltrating the image to a C2 server.7 By the end of 2017, an adversary group used Invoke-PSImage to hide PowerShell commands in an image file (png) and execute the code on a victim's system. In this particular case the PowerShell code downloaded another obfuscated script to gather intelligence from the victim's machine and communicate it back to the adversary.8


  • APT28 encrypted a .dll payload using RTL and a custom encryption algorithm.9 APT28 has also obfuscated payloads with base64 and XOR.10
  • APT3 obfuscates files or information to help evade defensive measures. 11
  • APT32 has used the Invoke-Obfuscation framework to obfuscate their PowerShell.1213
  • APT34 has used base64-encoded files that are dropped to victims.14
  • BlackOasis's first stage shellcode contains a NOP sled with alternative instructions that was likely designed to bypass antivirus tools.15
  • Dust Storm has encoded payloads with a single-byte XOR, both skipping the key itself and zeroing in an attempt to avoid exposing the key.16
  • Elderwood has encrypted documents and malicious executables.17
  • FIN7 has used fragmented strings, environment variables, standard input (stdin), and native character-replacement functionalities to obfuscate commmands.4
  • FIN8 has used environment variables and standard input (stdin) to obfuscate command-line arguments.4 FIN8 also obfuscates malicious macros delivered as payloads.18
  • Group5 disguised its malicious binaries with several layers of obfuscation, including encrypting the files.19
  • Lazarus Group malware uses multiple types of encryption and encoding in its malware files, including AES, Caracachs, RC4, basic XOR with constant 0xA7, and other techniques.20212223
  • Leviathan has obfuscated code using base64 and gzip compression.24
  • Magic Hound malware has used base64-encoded commands and files, and has also encrypted embedded strings with AES.25
  • MuddyWater has used Daniel Bohannon’s Invoke-Obfuscation framework.2613 The group also used files with base64 encoded PowerShell commands.27
  • OilRig has encrypted and encoded data in its malware.28
  • Droppers used by Putter Panda use RC4 or a 16-byte XOR key consisting of the bytes 0xA0 – 0xAF to obfuscate payloads.29
  • Most of the strings in ADVSTORESHELL are encrypted with an XOR-based algorithm; some strings are also encrypted with 3DES and reversed. API function names are also reversed, presumably to avoid detection in memory.309
  • CORESHELL obfuscates strings using a custom stream cipher.31
  • The payload of CozyCar is encrypted with simple XOR with a rotating key. The CozyCar configuration file has been encrypted with RC4 keys.32
  • hides any strings related to its own indicators of compromise.33
  • Daserf uses encrypted Windows APIs and also encrypts data using the alternative base64+RC4 or the Caesar cipher.34
  • The DustySky dropper uses a function to obfuscate the name of functions and other parts of the malware.35
  • Elise encrypts several of its files, including configuration files.36
  • Variants of Emissary encrypt payloads using various XOR ciphers, as well as a custom algorithm that uses the "srand" and "rand" functions.3738
  • Gazer logs its actions into files that are encrypted with 3DES. It also uses RSA to encrypt resources.39
  • H1N1 uses multiple techniques to obfuscate strings, including XOR.40
  • Some strings in HOMEFRY are obfuscated with XOR x56.41
  • HTTPBrowser's code may be obfuscated through structured exception handling and return-oriented programming.42
  • The Helminth config file is encrypted with RC4.43
  • Hi-Zor uses various XOR techniques to obfuscate its components.44
  • Hydraq uses basic obfuscation in the form of spaghetti code.4517
  • ISMInjector is obfuscated with the off-the-shelf SmartAssembly .NET obfuscator created by red-gate.com.46
  • Invoke-PSImage can be used to embed a PowerShell script within the pixels of a PNG file.47
  • Many strings in JHUHUGIT are obfuscated with a XOR algorithm.4849
  • A JPIN uses a encrypted and compressed payload that is disguised as a bitmap within the resource section of the installer.50
  • Matroyshka obfuscates API function names using a substitute cipher combined with Base64 encoding.51
  • OLDBAIT obfuscates internal strings and unpacks them at startup.31
  • Some Orz strings are base64 encoded, such as the embedded DLL known as MockDll.24
  • POSHSPY appends a file signature header (randomly selected from six file types) to encrypted data prior to upload or download.52
  • POWERSTATS uses character replacement, PowerShell environment variables, and XOR encoding to obfuscate code.27
  • PUNCHTRACK is loaded and executed by a highly obfuscated launcher.53
  • Pisloader obfuscates files by splitting strings into smaller sub-strings and including "garbage" strings that are never used. The malware also uses return-oriented programming (ROP) technique and single-byte XOR to obfuscate data.54
  • PowerDuke uses steganography to hide backdoors in PNG files, which are also encrypted using the Tiny Encryption Algorithm (TEA).1
  • PowerSploit contains a collection of ScriptModification modules that compress and encode scripts and payloads.5556
  • Some resources in Prikormka are encrypted with a simple XOR operation or encoded with Base64.57
  • RTM strings, network data, configuration, and modules are encrypted with a modified RC4 algorithm.58
  • Reaver encrypts some of its files with XOR.59
  • A RedLeaves configuration file is encrypted with a simple XOR key, 0x53.60
  • Some data in Remsec is encrypted using RC5 in CBC mode, AES-CBC with a hardcoded key, RC4, or Salsa20. Some data is also base64-encoded.6162
  • SHOTPUT is obscured using XOR encoding and appended to a valid GIF file.6364
  • ... further results


Ensure logging and detection mechanisms analyze commands after being processed/interpreted, rather than the raw input. Consider utilizing the Antimalware Scan Interface (AMSI) on Windows 10 for this functionality.65

Mitigation of compressed and encrypted files sent over the network and through email may not be advised since it may impact normal operations.


Detection of file obfuscation is difficult unless artifacts are left behind by the obfuscation process that are uniquely detectable with a signature. If detection of the obfuscation itself is not possible, it may be possible to detect the malicious activity that caused the obfuscated file (for example, the method that was used to write, read, or modify the file on the file system).

Flag and analyze commands containing indicators of obfuscation and known suspicious syntax such as uninterpreted escape characters like ^ and ". Windows' Sysmon and Event ID 4688 displays command-line arguments for processes. Deobfuscation tools can be used to detect these indicators in files/payloads.66567

Obfuscation used in payloads for Initial Access can be detected at the network. Use network intrusion detection systems and email gateway filtering to identify compressed and encrypted attachments and scripts. Some email attachment detonation systems can open compressed and encrypted attachments. Payloads delivered over an encrypted connection from a website require encrypted network traffic inspection.


  1. a b  Adair, S.. (2016, November 9). PowerDuke: Widespread Post-Election Spear Phishing Campaigns Targeting Think Tanks and NGOs. Retrieved January 11, 2017.
  2. ^  Pierre-Marc Bureau. (2013, April 26). Linux/Cdorked.A: New Apache backdoor being used in the wild to serve Blackhole. Retrieved September 10, 2017.
  3. ^  Tedesco, B. (2016, September 23). Security Alert Summary. Retrieved February 12, 2018.
  4. a b c  Bohannon, D. & Carr N. (2017, June 30). Obfuscation in the Wild: Targeted Attackers Lead the Way in Evasion Techniques. Retrieved February 12, 2018.
  5. a b  Bohannon, D. & Holmes, L. (2017, July 27). Revoke-Obfuscation: PowerShell Obfuscation Detection Using Science. Retrieved February 12, 2018.
  6. ^  White, J. (2017, March 10). Pulling Back the Curtains on EncodedCommand PowerShell Attacks. Retrieved February 12, 2018.
  7. ^  Wikipedia. (2017, December 29). Duqu. Retrieved April 10, 2018.
  8. ^  Saavedra-Morales, J., Sherstobitoff, R. (2018, January 6). Malicious Document Targets Pyeongchang Olympics. Retrieved April 10, 2018.
  9. a b  Bitdefender. (2015, December). APT28 Under the Scope. Retrieved February 23, 2017.
  10. ^  Lee, B, et al. (2018, February 28). Sofacy Attacks Multiple Government Entities. Retrieved March 15, 2018.
  11. ^  Symantec Security Response. (2016, September 6). Buckeye cyberespionage group shifts gaze from US to Hong Kong. Retrieved September 26, 2016.
  12. ^  Carr, N.. (2017, May 14). Cyber Espionage is Alive and Well: APT32 and the Threat to Global Corporations. Retrieved June 18, 2017.
  13. a b  Bohannon, D.. (2017, March 13). Invoke-Obfuscation - PowerShell Obfuscator. Retrieved June 18, 2017.
  14. ^  Sardiwal, M, et al. (2017, December 7). New Targeted Attack in the Middle East by APT34, a Suspected Iranian Threat Group, Using CVE-2017-11882 Exploit. Retrieved December 20, 2017.
  15. ^  Kaspersky Lab's Global Research & Analysis Team. (2017, October 16). BlackOasis APT and new targeted attacks leveraging zero-day exploit. Retrieved February 15, 2018.
  16. ^  Gross, J. (2016, February 23). Operation Dust Storm. Retrieved September 19, 2017.
  17. a b  O'Gorman, G., and McDonald, G.. (2012, September 6). The Elderwood Project. Retrieved February 15, 2018.
  18. ^  Elovitz, S. & Ahl, I. (2016, August 18). Know Your Enemy: New Financially-Motivated & Spear-Phishing Group. Retrieved February 26, 2018.
  19. ^  Scott-Railton, J., et al. (2016, August 2). Group5: Syria and the Iranian Connection. Retrieved September 26, 2016.
  20. ^  Novetta Threat Research Group. (2016, February 24). Operation Blockbuster: Unraveling the Long Thread of the Sony Attack. Retrieved February 25, 2016.
  21. ^  Novetta Threat Research Group. (2016, February 24). Operation Blockbuster: Loaders, Installers and Uninstallers Report. Retrieved March 2, 2016.
  22. ^  Novetta Threat Research Group. (2016, February 24). Operation Blockbuster: Remote Administration Tools & Content Staging Malware Report. Retrieved March 16, 2016.
  23. ^  Sherstobitoff, R. (2018, February 12). Lazarus Resurfaces, Targets Global Banks and Bitcoin Users. Retrieved February 19, 2018.
  24. a b  Axel F, Pierre T. (2017, October 16). Leviathan: Espionage actor spearphishes maritime and defense targets. Retrieved February 15, 2018.
  25. ^  Lee, B. and Falcone, R. (2017, February 15). Magic Hound Campaign Attacks Saudi Targets. Retrieved December 27, 2017.
  26. ^  Lancaster, T.. (2017, November 14). Muddying the Water: Targeted Attacks in the Middle East. Retrieved March 15, 2018.
  27. a b  Singh, S. et al.. (2018, March 13). Iranian Threat Group Updates Tactics, Techniques and Procedures in Spear Phishing Campaign. Retrieved April 11, 2018.
  28. ^  Unit 42. (2017, December 15). Unit 42 Playbook Viewer - OilRig. Retrieved December 20, 2017.
  29. ^  Crowdstrike Global Intelligence Team. (2014, June 9). CrowdStrike Intelligence Report: Putter Panda. Retrieved January 22, 2016.
  30. ^  Kaspersky Lab's Global Research and Analysis Team. (2015, December 4). Sofacy APT hits high profile targets with updated toolset. Retrieved December 10, 2015.
  31. a b  FireEye. (2015). APT28: A WINDOW INTO RUSSIA’S CYBER ESPIONAGE OPERATIONS?. Retrieved August 19, 2015.
  32. ^  F-Secure Labs. (2015, April 22). CozyDuke: Malware Analysis. Retrieved December 10, 2015.
  33. ^  Hayashi, K. (2005, August 18). Backdoor.Darkmoon. Retrieved February 23, 2018.
  34. ^  Chen, J. and Hsieh, M. (2017, November 7). REDBALDKNIGHT/BRONZE BUTLER’s Daserf Backdoor Now Using Steganography. Retrieved December 27, 2017.
  1. ^  ClearSky. (2016, January 7). Operation DustySky. Retrieved January 8, 2016.
  2. ^  Falcone, R., et al.. (2015, June 16). Operation Lotus Blossom. Retrieved February 15, 2016.
  3. ^  Falcone, R. and Miller-Osborn, J.. (2015, December 18). Attack on French Diplomat Linked to Operation Lotus Blossom. Retrieved February 15, 2016.
  4. ^  Falcone, R. and Miller-Osborn, J.. (2016, February 3). Emissary Trojan Changelog: Did Operation Lotus Blossom Cause It to Evolve?. Retrieved February 15, 2016.
  5. ^  Kaspersky Lab's Global Research & Analysis Team. (2017, August 30). Introducing WhiteBear. Retrieved September 21, 2017.
  6. ^  Reynolds, J.. (2016, September 13). H1N1: Technical analysis reveals new capabilities. Retrieved September 26, 2016.
  7. ^  FireEye. (2018, March 16). Suspected Chinese Cyber Espionage Group (TEMP.Periscope) Targeting U.S. Engineering and Maritime Industries. Retrieved April 11, 2018.
  8. ^  Dell SecureWorks Counter Threat Unit Threat Intelligence. (2015, August 5). Threat Group-3390 Targets Organizations for Cyberespionage. Retrieved January 25, 2016.
  9. ^  Falcone, R. and Lee, B.. (2016, May 26). The OilRig Campaign: Attacks on Saudi Arabian Organizations Deliver Helminth Backdoor. Retrieved May 3, 2017.
  10. ^  Fidelis Cybersecurity. (2015, December 16). Fidelis Threat Advisory #1020: Dissecting the Malware Involved in the INOCNATION Campaign. Retrieved March 24, 2016.
  11. ^  Symantec Security Response. (2010, January 18). The Trojan.Hydraq Incident. Retrieved February 20, 2018.
  12. ^  Falcone, R. and Lee, B. (2017, October 9). OilRig Group Steps Up Attacks with New Delivery Documents and New Injector Trojan. Retrieved January 8, 2018.
  13. ^  Adams, B. (2017, December 17). Invoke-PSImage. Retrieved April 10, 2018.
  14. ^  F-Secure. (2015, September 8). Sofacy Recycles Carberp and Metasploit Code. Retrieved August 3, 2016.
  15. ^  ESET. (2016, October). En Route with Sednit - Part 1: Approaching the Target. Retrieved November 8, 2016.
  16. ^  Windows Defender Advanced Threat Hunting Team. (2016, April 29). PLATINUM: Targeted attacks in South and Southeast Asia. Retrieved February 15, 2018.
  17. ^  Minerva Labs LTD and ClearSky Cyber Security. (2015, November 23). CopyKittens Attack Group. Retrieved September 11, 2017.
  18. ^  Dunwoody, M.. (2017, April 3). Dissecting One of APT29’s Fileless WMI and PowerShell Backdoors (POSHSPY). Retrieved April 5, 2017.
  19. ^  Kizhakkinan, D. et al.. (2016, May 11). Threat Actor Leverages Windows Zero-day Exploit in Payment Card Data Attacks. Retrieved February 12, 2018.
  20. ^  Grunzweig, J., et al. (2016, May 24). New Wekby Attacks Use DNS Requests As Command and Control Mechanism. Retrieved August 17, 2016.
  21. ^  PowerShellMafia. (2012, May 26). PowerSploit - A PowerShell Post-Exploitation Framework. Retrieved February 6, 2018.
  22. ^  PowerSploit. (n.d.). PowerSploit. Retrieved February 6, 2018.
  23. ^  Cherepanov, A.. (2016, May 17). Operation Groundbait: Analysis of a surveillance toolkit. Retrieved May 18, 2016.
  24. ^  Faou, M. and Boutin, J.. (2017, February). Read The Manual: A Guide to the RTM Banking Trojan. Retrieved March 9, 2017.
  25. ^  Grunzweig, J. and Miller-Osborn, J. (2017, November 10). New Malware with Ties to SunOrcal Discovered. Retrieved November 16, 2017.
  26. ^  PwC and BAE Systems. (2017, April). Operation Cloud Hopper: Technical Annex. Retrieved April 13, 2017.
  27. ^  Symantec Security Response. (2016, August 8). Backdoor.Remsec indicators of compromise. Retrieved August 17, 2016.
  28. ^  Kaspersky Lab's Global Research & Analysis Team. (2016, August 9). The ProjectSauron APT. Technical Analysis. Retrieved August 17, 2016.
  29. ^  Eng, E., Caselden, D.. (2015, June 23). Operation Clandestine Wolf – Adobe Flash Zero-Day in APT3 Phishing Campaign. Retrieved January 14, 2016.
  30. ^  Falcone, R. and Wartell, R.. (2015, July 27). Observations on CVE-2015-3113, Prior Zero-Days and the Pirpi Payload. Retrieved January 22, 2016.
  31. ^  Microsoft. (2015, June 9). Windows 10 to offer application developers new malware defenses. Retrieved February 12, 2018.
  32. ^  Bohannon, D. (2017, July 27). Revoke-Obfuscation. Retrieved February 12, 2018.
  33. ^  Carr, N. (2016, August 14). OfficeCrackros. Retrieved February 12, 2018.