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T1562.003 - Impair Command History Logging

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T1562.003 - 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).

Atomic Tests#

Atomic Test #1 - Disable history collectionDisables history collection in shells#

Supported Platforms: linux, macos#### Attack Commands: Run with sh

export HISTCONTROL=ignoreboth
whoami

Invoke-AtomicTest T1562.003 -TestNumbers 1

Atomic Test #2 - Disable history collection (freebsd)Disables history collection in shells#

Supported Platforms: linux#### Attack Commands: Run with sh

export HISTSIZE=0
whoami

Invoke-AtomicTest T1562.003 -TestNumbers 2

Atomic Test #3 - Mac HISTCONTROLThe HISTCONTROL variable is set to ignore (not write to the history file) command that are a duplicate of something already in the history#

and commands that start with a space. This atomic sets this variable in the current session and also writes it to the current user’s ~/.bash_profile so that it will apply to all future settings as well. https://www.linuxjournal.com/content/using-bash-history-more-efficiently-histcontrol Supported Platforms: macos, linuxRun it with these steps!1. export HISTCONTROL=ignoreboth 2. echo export “HISTCONTROL=ignoreboth” >> ~/.bash_profile 3. ls 4. whoami > recon.txt

Atomic Test #4 - Clear bash historyAn attacker may clear the bash history cache and the history file as their last act before logging off to remove the record of their command line activities.#

In this test we use the \(HISTFILE variable throughout to 1. confirms the \)HISTFILE variable is set 2. echo “” into it 3..5 confirm the file is empty 6 clear the history cache 7. confirm the history cache is empty. This is when the attacker would logoff. Supported Platforms: linux Elevation Required (e.g. root or admin)#### Attack Commands: Run with bash

cp $HISTFILE $HISTFILE.OLD
if ((${#HISTFILE[@]})); then echo $HISTFILE; fi
echo "" > $HISTFILE
if [ $(wc -c <$HISTFILE) -gt 1 ]; then echo "$HISTFILE is larger than 1k"; fi
ls -la $HISTFILE 
cat $HISTFILE
history -c 
if [ $(history |wc -l) -eq 1 ]; then echo "History cache cleared"; fi

Invoke-AtomicTest T1562.003 -TestNumbers 4

Cleanup:#

mv -f $HISTFILE.OLD $HISTFILE 

Invoke-AtomicTest T1562.003 -TestNumbers 4 -Cleanup

Atomic Test #5 - Setting the HISTCONTROL environment variableAn attacker may exploit the space before a command (e.g. ” ls”) or the duplicate command suppression feature in Bash history to prevent their commands from being recorded in the history file or to obscure the order of commands used.#

In this test we 1. sets \(HISTCONTROL to ignoreboth 2. clears the history cache 3. executes ls -la with a space in-front of it 4. confirms that ls -la is not in the history cache 5. sets \)HISTCONTROL to erasedups 6. clears the history cache 7..9 executes ls -la $HISTFILE 3 times 10. confirms that their is only one command in history Supported Platforms: linux Elevation Required (e.g. root or admin)#### Attack Commands: Run with bash

TEST=$(echo $HISTCONTROL)
if [ "$HISTCONTROL" != "ignoreboth" ]; then export HISTCONTROL="ignoreboth"; fi
history -c 
ls -la $HISTFILE # " ls -la $HISTFILE"
if [ $(history |wc -l) -eq 1 ]; then echo "ls -la is not in history cache"; fi
# -> ls -la is not in history cache
if [ "$HISTCONTROL" != "erasedups" ]; then export HISTCONTROL="erasedups"; fi
history -c 
ls -la $HISTFILE
ls -la $HISTFILE
ls -la $HISTFILE
if [ $(history |wc -l) -eq 2 ]; then echo "Their is only one entry for ls -la $HISTFILE"; fi

Invoke-AtomicTest T1562.003 -TestNumbers 5

Cleanup:#

export HISTCONTROL=$(echo $TEST)

Invoke-AtomicTest T1562.003 -TestNumbers 5 -Cleanup

Atomic Test #6 - Setting the HISTFILESIZE environment variableAn Adversary may set the bash history files size environment variable (HISTFILESIZE) to zero to prevent the logging of commands to the history file after they log out of the system.#

Note: we don’t wish to log out, so we are just confirming the value of HISTFILESIZE. In this test we 1. echo HISTFILESIZE 2. set it to zero 3. confirm that HISTFILESIZE is set to zero. Supported Platforms: linux Elevation Required (e.g. root or admin)#### Attack Commands: Run with bash

TEST=$(echo $HISTFILESIZE)
echo $HISTFILESIZE
export HISTFILESIZE=0
if [ $(echo $HISTFILESIZE) -eq 0 ]; then echo "\$HISTFILESIZE is zero"; fi
# -> $HISTFILESIZE is zero

Invoke-AtomicTest T1562.003 -TestNumbers 6

Cleanup:#

export HISTCONTROL=$(echo $TEST)

Invoke-AtomicTest T1562.003 -TestNumbers 6 -Cleanup

Atomic Test #7 - Setting the HISTSIZE environment variableAn Adversary may set the sh history files size environment variable (HISTSIZE) to zero to prevent the logging of commands to the history file after they log out of the system.#

Note: we don’t wish to log out, so we are just confirming the value of HISTSIZE. In this test we 1. echo HISTSIZE 2. set it to zero 3. confirm that HISTSIZE is set to zero. Supported Platforms: linux Elevation Required (e.g. root or admin)#### Attack Commands: Run with sh

echo $HISTSIZE
export HISTSIZE=0
if [ $(echo $HISTSIZE) -eq 0 ]; then echo "\$HISTSIZE is zero"; fi
# -> $HISTSIZE is zero

Invoke-AtomicTest T1562.003 -TestNumbers 7

Cleanup:#

export HISTSIZE=100

Invoke-AtomicTest T1562.003 -TestNumbers 7 -Cleanup

Atomic Test #8 - Setting the HISTFILE environment variableAn Adversary may clear, unset or redirect the history environment variable HISTFILE to prevent logging of commands to the history file after they log out of the system.#

Note: we don’t wish to log out, so we are just confirming the value of HISTFILE. In this test we 1. echo HISTFILE 2. set it to /dev/null 3. confirm that HISTFILE is set to /dev/null. Supported Platforms: linux Elevation Required (e.g. root or admin)#### Attack Commands: Run with bash

TEST=$(echo $HISTFILE)
echo $HISTFILE
export HISTFILE="/dev/null"
if [ $(echo $HISTFILE) == "/dev/null" ]; then echo "\$HISTFILE is /dev/null"; fi
# -> $HISTFILE is /dev/null

Invoke-AtomicTest T1562.003 -TestNumbers 8

Cleanup:#

export HISTFILE=$(echo $TEST)

Invoke-AtomicTest T1562.003 -TestNumbers 8 -Cleanup

Atomic Test #9 - Setting the HISTFILE environment variable (freebsd)An Adversary may clear, unset or redirect the history environment variable HISTFILE to prevent logging of commands to the history file after they log out of the system.#

Note: we don’t wish to log out, so we are just confirming the value of HISTFILE. In this test we 1. echo HISTFILE 2. set it to /dev/null 3. confirm that HISTFILE is set to /dev/null. Supported Platforms: linux Elevation Required (e.g. root or admin)#### Attack Commands: Run with sh

echo $HISTFILE
export HISTFILE="/dev/null"
if [ $(echo $HISTFILE) == "/dev/null" ]; then echo "\$HISTFILE is /dev/null"; fi
# -> $HISTFILE is /dev/null

Invoke-AtomicTest T1562.003 -TestNumbers 9

Cleanup:#

export HISTFILE=~/.sh_history

Invoke-AtomicTest T1562.003 -TestNumbers 9 -Cleanup

Atomic Test #10 - Setting the HISTIGNORE environment variableAn 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. Supported Platforms: linux Elevation Required (e.g. root or admin)#### Attack Commands: Run with bash

if ((${#HISTIGNORE[@]})); then echo "\$HISTIGNORE = $HISTIGNORE"; else export HISTIGNORE='ls*:rm*:ssh*'; echo "\$HISTIGNORE = $HISTIGNORE"; fi
# -> $HISTIGNORE = ls*:rm*:ssh*
history -c 
ls -la $HISTFILE
ls -la ~/.bash_logout
if [ $(history |wc -l) -eq 1 ]; then echo "ls commands are not in history"; fi
# -> ls commands are not in history
unset HISTIGNORE

if ((${#HISTIGNORE[@]})); then echo "\$HISTIGNORE = $HISTIGNORE"; else export HISTIGNORE='*'; echo "\$HISTIGNORE = $HISTIGNORE"; fi
# -> $HISTIGNORE = *
history -c 
whoami
groups
if [ $(history |wc -l) -eq 0 ]; then echo "History cache is empty"; fi
# -> History cache is empty

Invoke-AtomicTest T1562.003 -TestNumbers 10

Cleanup:#

unset HISTIGNORE

Invoke-AtomicTest T1562.003 -TestNumbers 10 -Cleanup

Detection#

Correlating a user session with a distinct lack of new commands in their .bash_history can be a clue to suspicious behavior. Additionally, users checking or changing their HISTCONTROL, HISTFILE, or HISTFILESIZE environment variables may be suspicious.

Monitor for modification of PowerShell command history settings through processes being created with -HistorySaveStyle SaveNothing command-line arguments and use of the PowerShell commands Set-PSReadlineOption -HistorySaveStyle SaveNothing and Set-PSReadLineOption -HistorySavePath {File Path}. Further, Network Device CLI commands may also be used to clear or disable historical log data with built-in features native to the network device platform. Monitor such command activity for unexpected or unauthorized use of commands being run by non-standard users from non-standard locations.

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