Command and Scripting Interpreter: AppleScript
Adversaries may abuse AppleScript for execution. AppleScript is a macOS scripting language designed to control applications and parts of the OS via inter-application messages called AppleEvents. These AppleEvent messages can be sent independently or easily scripted with AppleScript. These events can locate open windows, send keystrokes, and interact with almost any open application locally or remotely.
Scripts can be run from the command-line via
osascript /path/to/script or
osascript -e "script here". Aside from the command line, scripts can be executed in numerous ways including Mail rules, Calendar.app alarms, and Automator workflows. AppleScripts can also be executed as plain text shell scripts by adding
#!/usr/bin/osascript to the start of the script file.
AppleScripts do not need to call
osascript to execute, however. They may be executed from within mach-O binaries by using the macOS Native APIs
OSAScript, both of which execute code independent of the
/usr/bin/osascript command line utility.
Adversaries may abuse AppleScript to execute various behaviors, such as interacting with an open SSH connection, moving to remote machines, and even presenting users with fake dialog boxes. These events cannot start applications remotely (they can start them locally), but they can interact with applications if they're already running remotely. On macOS 10.10 Yosemite and higher, AppleScript has the ability to execute Native APIs, which otherwise would require compilation and execution in a mach-O binary file format.. Since this is a scripting language, it can be used to launch more common techniques as well such as a reverse shell via Python.
Require that all AppleScript be signed by a trusted developer ID before being executed - this will prevent random AppleScript code from executing. This subjects AppleScript code to the same scrutiny as other .app files passing through Gatekeeper.
Use application control where appropriate.
Monitor for execution of AppleScript through
osascript and usage of the
OSAScript APIs that may be related to other suspicious behavior occurring on the system. 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.
Understanding standard usage patterns is important to avoid a high number of false positives. If scripting is restricted for normal users, then any attempts 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.
- Apple. (2016, January 25). Introduction to AppleScript Language Guide. Retrieved March 28, 2020.
- Phil Stokes. (2020, March 16). How Offensive Actors Use AppleScript For Attacking macOS. Retrieved July 17, 2020.
- Phil Stokes. (2019, December 5). macOS Red Team: Calling Apple APIs Without Building Binaries. Retrieved July 17, 2020.
- Yerko Grbic. (2017, February 14). Macro Malware Targets Macs. Retrieved July 8, 2017.
- Sushko, O. (2019, April 17). macOS Bundlore: Mac Virus Bypassing macOS Security Features. Retrieved June 30, 2020.
- Patrick Wardle. (n.d.). Mac Malware of 2017. Retrieved September 21, 2018.
- Steven Sande. (2013, December 23). AppleScript and Automator gain new features in OS X Mavericks. Retrieved September 21, 2018.