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 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.
Adds a command to the .bash_profile file of the current user
Supported Platforms: macOS, Linux
auto_generated_guid: 94500ae1-7e31-47e3-886b-c328da46872f
| Name | Description | Type | Default Value | |——|————-|——|—————| | command_to_add | Command to add to the .bash_profile file | string | echo “Hello from Atomic Red Team T1546.004” > /tmp/T1546.004|
1
sh
!1
echo '#{command_to_add}' >> ~/.bash_profile
1
2
head -n '-2' ~/.bash_profile > /tmp/T1546.004
mv /tmp/T1546.004 ~/.bash_profile
Adds a command to the .bashrc file of the current user
Supported Platforms: macOS, Linux
auto_generated_guid: 0a898315-4cfa-4007-bafe-33a4646d115f
| Name | Description | Type | Default Value | |——|————-|——|—————| | command_to_add | Command to add to the .bashrc file | string | echo “Hello from Atomic Red Team T1546.004” > /tmp/T1546.004|
1
sh
!1
echo '#{command_to_add}' >> ~/.bashrc
1
2
head -n '-2' ~/.bashrc > /tmp/T1546.004
mv /tmp/T1546.004 ~/.bashrc
Adds a command to the .shrc file of the current user
Supported Platforms: Linux
auto_generated_guid: 41502021-591a-4649-8b6e-83c9192aff53
| Name | Description | Type | Default Value | |——|————-|——|—————| | command_to_add | Command to add to the .shrc file | string | echo “Hello from Atomic Red Team T1546.004” > /tmp/T1546.004|
1
sh
!1
echo '#{command_to_add}' >> ~/.shrc
1
2
head -n '-2' ~/.shrc > /tmp/T1546.004
mv /tmp/T1546.004 ~/.shrc
An adversary may wish to establish persistence by executing malicious commands from the systems /etc/profile every time “any” user logs in.
Supported Platforms: Linux
auto_generated_guid: 694b3cc8-6a78-4d35-9e74-0123d009e94b
| Name | Description | Type | Default Value | |——|————-|——|—————| | text_to_append | Text to append to the /etc/profile file | string | # Hello from Atomic Red Team T1546.004|
1
sh
! Elevation Required (e.g. root or admin)1
echo '#{text_to_append}' >> /etc/profile
1
sed -i "s/# Atomic Red Team was here! T1546.004//" /etc/profile
An adversary may wish to establish persistence by executing malicious commands from the users ~/.profile every time the “user” logs in.
Supported Platforms: Linux
auto_generated_guid: bbdb06bc-bab6-4f5b-8232-ba3fbed51d77
| Name | Description | Type | Default Value | |——|————-|——|—————| | text_to_append | Text to append to the ~/.profile file | string | # Atomic Red Team was here… T1546.004|
1
sh
!1
echo '#{text_to_append}' >> ~/.profile
1
sed -i "s/# Atomic Red Team was here... T1546.004//" ~/.profile
An adversary may wish to establish persistence by adding commands into any of the script files in the /etc/profile.d/ directory, which are executed every time “any” user logs in.
Supported Platforms: Linux
auto_generated_guid: 8fe2ccfd-f079-4c03-b1a9-bd9b362b67d4
| Name | Description | Type | Default Value | |——|————-|——|—————| | text_to_append | Text to append to the /etc/profile.d/bash_completion.sh file | string | # Atomic Red Team was here… T1546.004|
1
sh
! Elevation Required (e.g. root or admin)1
echo '#{text_to_append}' >> /etc/profile.d/bash_completion.sh
1
sed -i "s/# Atomic Red Team was here... T1546.004//" /etc/profile.d/bash_completion.sh
The Bash shell runs ~/.bash_logout “if it exists” to run commands on user logout. An adversary may create or append to a .bash_logout to clear history, start processes etc. Note the ~/.bash_logout is only run if you explicitly exit or log out of an “interactive login shell session” i.e. via the console, SSH, /bin/bash -l or su -l
This test creates the art user, logs in, creates a .bash_logout which will echo some text into the art.txt file on logout and logs out and the /home/art/art.txt is created.
Supported Platforms: Linux
auto_generated_guid: 37ad2f24-7c53-4a50-92da-427a4ad13f58
1
bash
! Elevation Required (e.g. root or admin)1
2
useradd --create-home --shell /bin/bash art
su -l art -c "echo 'echo \"Atomic Red Team was here... T1546.004\" >> /home/art/art.txt' >> /home/art/.bash_logout; exit"
1
userdel -fr art