Find sigma rule
Attack: Impair Defenses: Impair Command History Logging
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.
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
.(Citation: Microsoft PowerShell Command History)(Citation: Sophos PowerShell command audit)(Citation: Sophos PowerShell Command History Forensics)
Adversaries may also leverage a Network Device CLI on network devices to disable historical command logging (e.g. no logging
).
MITRE
Tactic
- defense-evasion
technique
- T1562.003
Test : Setting the HISTIGNORE environment variable
OS
- linux
Description:
An Adversary may take advantage of the HISTIGNORE environment variable either to ignore particular commands or all commands.
In this test we 1. set HISTIGNORE to ignore ls, rm and ssh commands 2. clear this history cache 3..4 execute ls commands 5. confirm that the ls commands are not in the history cache 6. unset HISTIGNORE variable 7.. same again, but ignoring ALL commands.
Executor
bash