Adversaries may impair command history logging to hide commands they run on a compromised system. Various command interpreters keep track of the commands users type in their terminal so that users can retrace what they've done.
On Linux and macOS, command history is tracked in a file pointed to by the environment variable HISTFILE. When a user logs off a system, this information is flushed to a file in the user's home directory called ~/.bash_history. The HISTCONTROL environment variable keeps track of what should be saved by the history command and eventually into the ~/.bash_history file when a user logs out. HISTCONTROL does not exist by default on macOS, but can be set by the user and will be respected. The HISTFILE environment variable is also used in some ESXi systems.[1]
Adversaries may clear the history environment variable (unset HISTFILE) or set the command history size to zero (export HISTFILESIZE=0) to prevent logging of commands. Additionally, HISTCONTROL can be configured to ignore commands that start with a space by simply setting it to "ignorespace". HISTCONTROL can also be set to ignore duplicate commands by setting it to "ignoredups". In some Linux systems, this is set by default to "ignoreboth" which covers both of the previous examples. This means that " ls" will not be saved, but "ls" would be saved by history. Adversaries can abuse this to operate without leaving traces by simply prepending a space to all of their terminal commands.
On Windows systems, the PSReadLine module tracks commands used in all PowerShell sessions and writes them to a file ($env:APPDATA\Microsoft\Windows\PowerShell\PSReadLine\ConsoleHost_history.txt by default). Adversaries may change where these logs are saved using Set-PSReadLineOption -HistorySavePath {File Path}. This will cause ConsoleHost_history.txt to stop receiving logs. Additionally, it is possible to turn off logging to this file using the PowerShell command Set-PSReadlineOption -HistorySaveStyle SaveNothing.[2][3][4]
Adversaries may also leverage a Network Device CLI on network devices to disable historical command logging (e.g. no logging).
| ID | Name | Description |
|---|---|---|
| G0082 | APT38 |
APT38 has prepended a space to all of their terminal commands to operate without leaving traces in the HISTCONTROL environment.[5] |
| C0046 | ArcaneDoor |
ArcaneDoor included disabling logging on targeted Cisco ASA appliances.[6][7] |
| S1161 | BPFDoor |
BPFDoor sets the |
| S1186 | Line Dancer |
Line Dancer can disable syslog on compromised devices.[6] |
| G1051 | Medusa Group |
Medusa Group has removed PowerShell command history through the use of the PSReadLine module by running the PowerShell command |
| C0056 | RedPenguin |
During RedPenguin, UNC3886 used malware to clear the |
| G1041 | Sea Turtle |
Sea Turtle unset the Bash and MySQL history files on victim systems.[12] |
| S0692 | SILENTTRINITY |
SILENTTRINITY can bypass ScriptBlock logging to execute unmanaged PowerShell code from memory.[13] |
| G1048 | UNC3886 |
UNC3886 has tampered with and disabled logging services on targeted systems.[14] |
| S1217 | VIRTUALPITA |
VIRTUALPITA can impair logging by setting the |
| ID | Mitigation | Description |
|---|---|---|
| M1039 | Environment Variable Permissions |
Prevent users from changing the |
| M1028 | Operating System Configuration |
Make sure that the |
| ID | Name | Analytic ID | Analytic Description |
|---|---|---|---|
| DET0563 | Detection Strategy for Impair Defenses via Impair Command History Logging across OS platforms. | AN1555 |
Detection of environment variable tampering (HISTFILE, HISTCONTROL, HISTFILESIZE) and absence of expected bash history writes. Correlation of unset or zeroed history variables with active shell sessions is indicative of adversarial evasion. |
| AN1556 |
Detection of bash/zsh history suppression via HISTFILE/HISTCONTROL manipulation and absence of ~/.bash_history updates. Observing environment variable changes tied to terminal processes is a strong indicator. |
||
| AN1557 |
Detection of PowerShell history suppression using Set-PSReadLineOption with SaveNothing or altered HistorySavePath. Correlating these options with PowerShell usage highlights adversarial evasion attempts. |
||
| AN1558 |
Detection of unset HISTFILE or modified history variables in ESXi shell sessions. Correlation of suspicious shell sessions with no recorded commands despite active usage. |
||
| AN1559 |
Detection of CLI commands that disable history logging such as 'no logging'. Anomalous lack of new commands in session logs while activity persists is a strong signal. |