Description
Adversaries may establish persistence through executing malicious commands triggered by a user’s shell. User Unix Shells execute several configuration scripts at different points throughout the session based on events. For example, when a user opens a command-line interface or remotely logs in (such as via SSH) a login shell is initiated. The login shell executes scripts from the system (/etc) and the user’s home directory (~/) to configure the environment. All login shells on a system use /etc/profile when initiated. These configuration scripts run at the permission level of their directory and are often used to set environment variables, create aliases, and customize the user’s environment. When the shell exits or terminates, additional shell scripts are executed to ensure the shell exits appropriately.
Adversaries may attempt to establish persistence by inserting commands into scripts automatically executed by shells. Using bash as an example, the default shell for most GNU/Linux systems, adversaries may add commands that launch malicious binaries into the /etc/profile and /etc/profile.d files.(Citation: intezer-kaiji-malware)(Citation: bencane blog bashrc) These files typically require root permissions to modify and are executed each time any shell on a system launches. For user level permissions, adversaries can insert malicious commands into ~/.bash_profile, ~/.bash_login, or ~/.profile which are sourced when a user opens a command-line interface or connects remotely.(Citation: anomali-rocke-tactics)(Citation: Linux manual bash invocation) Since the system only executes the first existing file in the listed order, adversaries have used ~/.bash_profile to ensure execution. Adversaries have also leveraged the ~/.bashrc file which is additionally executed if the connection is established remotely or an additional interactive shell is opened, such as a new tab in the command-line interface.(Citation: Tsunami)(Citation: anomali-rocke-tactics)(Citation: anomali-linux-rabbit)(Citation: Magento) Some malware targets the termination of a program to trigger execution, adversaries can use the ~/.bash_logout file to execute malicious commands at the end of a session.
For macOS, the functionality of this technique is similar but may leverage zsh, the default shell for macOS 10.15+. When the Terminal.app is opened, the application launches a zsh login shell and a zsh interactive shell. The login shell configures the system environment using /etc/profile, /etc/zshenv, /etc/zprofile, and /etc/zlogin.(Citation: ScriptingOSX zsh)(Citation: PersistentJXA_leopitt)(Citation: code_persistence_zsh)(Citation: macOS MS office sandbox escape) The login shell then configures the user environment with ~/.zprofile and ~/.zlogin. The interactive shell uses the ~/.zshrc to configure the user environment. Upon exiting, /etc/zlogout and ~/.zlogout are executed. For legacy programs, macOS executes /etc/bashrc on startup.
Platforms
Mitigations (1)
Restrict File and Directory PermissionsM1022
Making these files immutable and only changeable by certain administrators will limit the ability for adversaries to easily create user level persistence.
Threat Groups (1)
| ID | Group | Context |
|---|---|---|
| G1052 | Contagious Interview | [Contagious Interview](https://attack.mitre.org/groups/G1052) has targeted macOS victim hosts using a bash downloader `coremedia.sh` and a bash script... |
Associated Software (5)
| ID | Name | Type | Context |
|---|---|---|---|
| S1078 | RotaJakiro | Malware | When executing with non-root level permissions, [RotaJakiro](https://attack.mitre.org/software/S1078) can install persistence by adding a command to t... |
| S0362 | Linux Rabbit | Malware | [Linux Rabbit](https://attack.mitre.org/software/S0362) maintains persistence on an infected machine through rc.local and .bashrc files. (Citation: An... |
| S0690 | Green Lambert | Malware | [Green Lambert](https://attack.mitre.org/software/S0690) can establish persistence on a compromised host through modifying the `profile`, `login`, and... |
| S9014 | PHASEJAM | Malware | [PHASEJAM](https://attack.mitre.org/software/S9014) has used a bash script to modify components on Ivanti Connect Secure appliances and execute files ... |
| S0658 | XCSSET | Malware | Using [AppleScript](https://attack.mitre.org/techniques/T1059/002), [XCSSET](https://attack.mitre.org/software/S0658) adds it's executable to the user... |
References
- Anomali Threat Research. (2018, December 6). Pulling Linux Rabbit/Rabbot Malware Out of a Hat. Retrieved December 17, 2020.
- Anomali Threat Research. (2019, October 15). Illicit Cryptomining Threat Actor Rocke Changes Tactics, Now More Difficult to Detect. Retrieved December 17, 2020.
- ArchWiki. (2021, January 19). Bash. Retrieved February 25, 2021.
- Armin Briegel. (2019, June 5). Moving to zsh, part 2: Configuration Files. Retrieved February 25, 2021.
- Benjamin Cane. (2013, September 16). Understanding a little more about /etc/profile and /etc/bashrc. Retrieved September 25, 2024.
- Cedric Owens. (2021, May 22). macOS MS Office Sandbox Brain Dump. Retrieved August 20, 2021.
- Cesar Anjos. (2018, May 31). Shell Logins as a Magento Reinfection Vector. Retrieved December 17, 2020.
- Claud Xiao and Cong Zheng. (2017, April 6). New IoT/Linux Malware Targets DVRs, Forms Botnet. Retrieved December 17, 2020.
- Leo Pitt. (2020, August 6). Persistent JXA - A poor man's Powershell for macOS. Retrieved January 11, 2021.
- Leo Pitt. (2020, November 11). Github - PersistentJXA/BashProfilePersist.js. Retrieved January 11, 2021.
Frequently Asked Questions
What is T1546.004 (Unix Shell Configuration Modification)?
T1546.004 is a MITRE ATT&CK technique named 'Unix Shell Configuration Modification'. It belongs to the Privilege Escalation, Persistence tactic(s). Adversaries may establish persistence through executing malicious commands triggered by a user’s shell. User [Unix Shell](https://attack.mitre.org/techniques/T1059/004)s execute several configuration...
How can T1546.004 be detected?
Detection of T1546.004 (Unix Shell Configuration Modification) typically involves monitoring system logs, network traffic, and endpoint telemetry. Use SIEM rules, EDR solutions, and behavioral analytics to identify suspicious activity associated with this technique.
What mitigations exist for T1546.004?
There are 1 documented mitigations for T1546.004. Key mitigations include: Restrict File and Directory Permissions.
Which threat groups use T1546.004?
Known threat groups using T1546.004 include: Contagious Interview.