Command and Scripting Interpreter: Unix Shell

Adversaries may abuse Unix shell commands and scripts for execution. Unix shells are the primary command prompt on Linux and macOS systems, though many variations of the Unix shell exist (e.g. sh, bash, zsh, etc.) depending on the specific OS or distribution.[1][2] Unix shells can control every aspect of a system, with certain commands requiring elevated privileges.

Unix shells also support scripts that enable sequential execution of commands as well as other typical programming operations such as conditionals and loops. Common uses of shell scripts include long or repetitive tasks, or the need to run the same set of commands on multiple systems.

Adversaries may abuse Unix shells to execute various commands or payloads. Interactive shells may be accessed through command and control channels or during lateral movement such as with SSH. Adversaries may also leverage shell scripts to deliver and execute multiple commands on victims or as part of payloads used for persistence.

ID: T1059.004
Sub-technique of:  T1059
Tactic: Execution
Platforms: Linux, macOS
Permissions Required: User, root
Data Sources: Command: Command Execution, Process: Process Creation
Version: 1.0
Created: 09 March 2020
Last Modified: 15 June 2020

Procedure Examples

ID Name Description
S0504 Anchor

Anchor can execute payloads via shell scripting.[3]

S0584 AppleJeus

AppleJeus has used shell scripts to execute commands after installation and set persistence mechanisms.[4]

G0096 APT41

APT41 executed file /bin/pwd in activity exploiting CVE-2019-19781 against Citrix devices.[5]

S0482 Bundlore

Bundlore has leveraged /bin/sh and /bin/bash to execute commands on the victim machine.[6]

S0077 CallMe

CallMe has the capability to create a reverse shell on victims.[7]

S0220 Chaos

Chaos provides a reverse shell connection on 8338/TCP, encrypted via AES.[8]

S0369 CoinTicker

CoinTicker executes a bash script to establish a reverse shell.[9]

S0492 CookieMiner

CookieMiner has used a Unix shell script to run a series of commands targeting macOS.[10]

S0021 Derusbi

Derusbi is capable of creating a remote Bash shell and executing commands.[11][12]

S0600 Doki

Doki has executed shell scripts with /bin/sh.[13]

S0502 Drovorub

Drovorub can execute arbitrary commands as root on a compromised system.[14]

S0401 Exaramel for Linux

Exaramel for Linux has a command to execute a shell command on the system.[15][16]

S0410 Fysbis

Fysbis has the ability to create and execute commands in a remote shell for CLI.[17]

S0601 Hildegard

Hildegard has used shell scripts for execution.[18]

S0265 Kazuar

Kazuar uses /bin/bash to execute commands on the victim’s machine.[19]

S0599 Kinsing

Kinsing has used Unix shell scripts to execute commands in the victim environment.[20]

S0451 LoudMiner

LoudMiner used shell scripts to launch various services and to start/stop the QEMU virtualization.[21]

S0198 NETWIRE

NETWIRE has the ability to use /bin/bash and /bin/sh to execute commands.[22][23]

S0402 OSX/Shlayer

OSX/Shlayer can use bash scripts to check the macOS version and download payloads.[24]

S0352 OSX_OCEANLOTUS.D

OSX_OCEANLOTUS.D can use shell script to execute malicious code.[25]

S0587 Penquin

Penquin can execute remote commands using bash scripts.[26]

S0279 Proton

Proton uses macOS' .command file type to script actions.[27]

G0106 Rocke

Rocke used shell scripts to run commands which would obtain persistence and execute the cryptocurrency mining malware.[28]

S0468 Skidmap

Skidmap has used pm.sh to download and install its main payload.[29]

S0466 WindTail

WindTail can use the open command to execute an application.[30]

Mitigations

ID Mitigation Description
M1038 Execution Prevention

Use application control where appropriate.

Detection

Unix shell usage may be common on administrator, developer, or power user systems, depending on job function. If scripting is restricted for normal users, then any attempt 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.

Scripts are likely to perform actions with various effects on a system that may generate events, depending on the types of monitoring used. Monitor processes and command-line arguments for script execution and subsequent behavior. Actions may be related to network and system information discovery, collection, or other scriptable post-compromise behaviors and could be used as indicators of detection leading back to the source script.

References

  1. die.net. (n.d.). bash(1) - Linux man page. Retrieved June 12, 2020.
  2. Apple. (2020, January 28). Use zsh as the default shell on your Mac. Retrieved June 12, 2020.
  3. Grange, W. (2020, July 13). Anchor_dns malware goes cross platform. Retrieved September 10, 2020.
  4. Cybersecurity and Infrastructure Security Agency. (2021, February 21). AppleJeus: Analysis of North Korea’s Cryptocurrency Malware. Retrieved March 1, 2021.
  5. Glyer, C, et al. (2020, March). This Is Not a Test: APT41 Initiates Global Intrusion Campaign Using Multiple Exploits. Retrieved April 28, 2020.
  6. Sushko, O. (2019, April 17). macOS Bundlore: Mac Virus Bypassing macOS Security Features. Retrieved June 30, 2020.
  7. Falcone, R. and Miller-Osborn, J.. (2016, January 24). Scarlet Mimic: Years-Long Espionage Campaign Targets Minority Activists. Retrieved February 10, 2016.
  8. Sebastian Feldmann. (2018, February 14). Chaos: a Stolen Backdoor Rising Again. Retrieved March 5, 2018.
  9. Thomas Reed. (2018, October 29). Mac cryptocurrency ticker app installs backdoors. Retrieved April 23, 2019.
  10. Chen, y., et al. (2019, January 31). Mac Malware Steals Cryptocurrency Exchanges’ Cookies. Retrieved July 22, 2020.
  11. Fidelis Cybersecurity. (2016, February 29). The Turbo Campaign, Featuring Derusbi for 64-bit Linux. Retrieved March 2, 2016.
  12. FireEye. (2018, March 16). Suspected Chinese Cyber Espionage Group (TEMP.Periscope) Targeting U.S. Engineering and Maritime Industries. Retrieved April 11, 2018.
  13. Fishbein, N., Kajiloti, M.. (2020, July 28). Watch Your Containers: Doki Infecting Docker Servers in the Cloud. Retrieved March 30, 2021.
  14. NSA/FBI. (2020, August). Russian GRU 85th GTsSS Deploys Previously Undisclosed Drovorub Malware. Retrieved August 25, 2020.
  15. Cherepanov, A., Lipovsky, R. (2018, October 11). New TeleBots backdoor: First evidence linking Industroyer to NotPetya. Retrieved November 27, 2018.
  1. ANSSI. (2021, January 27). SANDWORM INTRUSION SET CAMPAIGN TARGETING CENTREON SYSTEMS. Retrieved March 30, 2021.
  2. Bryan Lee and Rob Downs. (2016, February 12). A Look Into Fysbis: Sofacy’s Linux Backdoor. Retrieved September 10, 2017.
  3. Chen, J. et al. (2021, February 3). Hildegard: New TeamTNT Cryptojacking Malware Targeting Kubernetes. Retrieved April 5, 2021.
  4. Levene, B, et al. (2017, May 03). Kazuar: Multiplatform Espionage Backdoor with API Access. Retrieved July 17, 2018.
  5. Singer, G. (2020, April 3). Threat Alert: Kinsing Malware Attacks Targeting Container Environments. Retrieved April 1, 2021.
  6. Malik, M. (2019, June 20). LoudMiner: Cross-platform mining in cracked VST software. Retrieved May 18, 2020.
  7. Lambert, T. (2020, January 29). Intro to Netwire. Retrieved January 7, 2021.
  8. Proofpoint. (2020, December 2). Geofenced NetWire Campaigns. Retrieved January 7, 2021.
  9. Carbon Black Threat Analysis Unit. (2019, February 12). New macOS Malware Variant of Shlayer (OSX) Discovered. Retrieved August 8, 2019.
  10. Magisa, L. (2020, November 27). New MacOS Backdoor Connected to OceanLotus Surfaces. Retrieved December 2, 2020.
  11. Leonardo. (2020, May 29). MALWARE TECHNICAL INSIGHT TURLA “Penquin_x64”. Retrieved March 11, 2021.
  12. Patrick Wardle. (n.d.). Mac Malware of 2017. Retrieved September 21, 2018.
  13. Liebenberg, D.. (2018, August 30). Rocke: The Champion of Monero Miners. Retrieved May 26, 2020.
  14. Remillano, A., Urbanec, J. (2019, September 19). Skidmap Linux Malware Uses Rootkit Capabilities to Hide Cryptocurrency-Mining Payload. Retrieved June 4, 2020.
  15. Wardle, Patrick. (2018, December 20). Middle East Cyber-Espionage analyzing WindShift's implant: OSX.WindTail (part 1). Retrieved October 3, 2019.