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. 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.
|Exaramel for Linux|
Use application control where appropriate.
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.
- die.net. (n.d.). bash(1) - Linux man page. Retrieved June 12, 2020.
- Apple. (2020, January 28). Use zsh as the default shell on your Mac. Retrieved June 12, 2020.
- Grange, W. (2020, July 13). Anchor_dns malware goes cross platform. Retrieved September 10, 2020.
- Glyer, C, et al. (2020, March). This Is Not a Test: APT41 Initiates Global Intrusion Campaign Using Multiple Exploits. Retrieved April 28, 2020.
- Sushko, O. (2019, April 17). macOS Bundlore: Mac Virus Bypassing macOS Security Features. Retrieved June 30, 2020.
- Falcone, R. and Miller-Osborn, J.. (2016, January 24). Scarlet Mimic: Years-Long Espionage Campaign Targets Minority Activists. Retrieved February 10, 2016.
- Sebastian Feldmann. (2018, February 14). Chaos: a Stolen Backdoor Rising Again. Retrieved March 5, 2018.
- Thomas Reed. (2018, October 29). Mac cryptocurrency ticker app installs backdoors. Retrieved April 23, 2019.
- Chen, y., et al. (2019, January 31). Mac Malware Steals Cryptocurrency Exchanges’ Cookies. Retrieved July 22, 2020.
- Fidelis Cybersecurity. (2016, February 29). The Turbo Campaign, Featuring Derusbi for 64-bit Linux. Retrieved March 2, 2016.
- FireEye. (2018, March 16). Suspected Chinese Cyber Espionage Group (TEMP.Periscope) Targeting U.S. Engineering and Maritime Industries. Retrieved April 11, 2018.
- NSA/FBI. (2020, August). Russian GRU 85th GTsSS Deploys Previously Undisclosed Drovorub Malware. Retrieved August 25, 2020.
- Cherepanov, A., Lipovsky, R. (2018, October 11). New TeleBots backdoor: First evidence linking Industroyer to NotPetya. Retrieved November 27, 2018.
- Bryan Lee and Rob Downs. (2016, February 12). A Look Into Fysbis: Sofacy’s Linux Backdoor. Retrieved September 10, 2017.
- Levene, B, et al. (2017, May 03). Kazuar: Multiplatform Espionage Backdoor with API Access. Retrieved July 17, 2018.
- Malik, M. (2019, June 20). LoudMiner: Cross-platform mining in cracked VST software. Retrieved May 18, 2020.
- Carbon Black Threat Analysis Unit. (2019, February 12). New macOS Malware Variant of Shlayer (OSX) Discovered. Retrieved August 8, 2019.
- Patrick Wardle. (n.d.). Mac Malware of 2017. Retrieved September 21, 2018.
- Liebenberg, D.. (2018, August 30). Rocke: The Champion of Monero Miners. Retrieved May 26, 2020.
- Remillano, A., Urbanec, J. (2019, September 19). Skidmap Linux Malware Uses Rootkit Capabilities to Hide Cryptocurrency-Mining Payload. Retrieved June 4, 2020.
- Wardle, Patrick. (2018, December 20). Middle East Cyber-Espionage analyzing WindShift's implant: OSX.WindTail (part 1). Retrieved October 3, 2019.