HTB - Blackfield

Overview

Short description to include any strange things to be dealt with

Useful Skills and Tools

Useful thing 1

  • description with generic example

Useful thing 2

  • description with generic example

Enumeration

Nmap scan

I started my enumeration with an nmap scan of 10.10.10.192. The options I regularly use are: -p-, which is a shortcut which tells nmap to scan all ports, -sC is the equivalent to --script=default and runs a collection of nmap enumeration scripts against the target, -sV does a service scan, and -oA <name> saves the output with a filename of <name>.

At first my scan wouldn't go through until I added the -Pn flag to stop nmap from sending ICMP probes. After that it proceeded normally.

Since port 445 (SMB) is open I tried to enumerate open shares by using anonymous login

with crackmapexec was unable to get any shares without a username, but I'm not sure if you can do anonymous login with this program so I tried with the standard smbclient as well

with smbclient got a list of shares!

I was able to login to the forensic share anonymously but was not allowed to do much

Trying again with the profiles$ share yielded a lot more information! I took all of the these usernames and added them to a list.

I tried using Metasploit's auxiliary(gather/kerberos_enumusers) Kerberos user enumeration tool, however I just got an error for each user saying [*] 10.10.10.193:88 - Wrong DOMAIN Name? Check DOMAIN and retry...

After trying numerous commands, I was able to at least verify that blackfield was indeed the correct domain name.

since the module in msfconsole didn't I decided to try the python-based Impacket script GetNPUsers.py which does the same type of check to see if any users have UF_DONT_REQUIRE_PREAUTH turned off.

I found three users that had this turned off, and one even had the password hash attached! Time to fire up hashcat.

After searching for the correct hash type I fired up hashcat and very quickly cracked the password using the rockyou.txt wordlist. The password for support was #00^BlackKnight

Initial Foothold

Road to User

The user support could view the same shares as I could see anonymously. Next I tried to see if this user could get any more information from them.

I connected to each of the three shares: profiles$ still had the same empty user directories, NETLOGON was completely empty, while SYSVOL only had a few files, none of which contained anything useful.

I ran ldapsearch next to see if I could get any more information than before, and a mountain of data returned. (I also made the mistake of not sending the output to a file the first time and my screen exploded). Unfortunately, there was nothing new or useful in all of that the output (besides a slew of anonymous sounding usernames such as blackfield123456, etc.)

With so many users to go off and no way to directly tell what rights I had with the user support I loaded bloodhound up to see if it could sniff me a path forward. The python version of bloodhound allows it to be run against a remote host with credentials, and outputs a few .json files that I imported into the main program.

Bloodhound reported 342 (!) users on this domain.

Most of them were named generically BLACKFIELD123456, however there were a few that stuck out. I set these as my targets and began looking for ways to link them. Since I already had the credentials for support I marked that user as 'owned' and proceeded to see what I could do with its access.

Since support has the ForceChangePassword privilege over the user audit2020 I looked up how to change a user's password via SMB and found: https://www.dark-hamster.com/operating-system/linux/ubuntu/reset-samba-user-password-via-command-line/

Unfortunately this did not work, so I did some searching to see if there was another way to do it remotely. I found a shady looking site that explained what I was looking for using RPC at https://malicious.link/post/2017/reset-ad-user-password-with-linux/ (it was mixed in the middle of a bunch of those scam/malware .it sites so I was a bit leery at first.)

This site showed that using rpcclient with the syntax rpcclient $> setuserinfo2 adminuser 23 'ASDqwe123' you could change a user's password without knowing the current one. It linked to a MSDN site which explained why to use 23 for the property. https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-samr/6b0dff90-5ac0-429a-93aa-150334adabf6?redirectedfrom=MSDN

3 pictures

I also tried doing it the 'easy' way with the one-liner from the bottom of the blog post and successfully changed it with the net command. I'll definitely have to remember that I can use net commands from Linux in the future!

now that I had a usable password for another user I set out to see what I could get into. I was unable to use WinRM or get anything further from rpcclient, so I went back to enumerating the open SMB shares.

ran mimikatz - python edition (pypykatz) on the lssas.DMP file, then pulled out the usernames, passwords, and hashes

I tried cracking the NTLM hashes with hashcat but even using all of the various rules and some basic mangles I was unsiccessful. Luckily since this is Windows domain I can try to do a pass-the-hash attack instead.

It didn't take long to find a valid combination. The password (hash) for svc_backup was 9658d1d1dcd9250115e2205d9f48400d. Luckily for me, this user is in the Windows Remote Management group, and port 5985 for WinRM was open. I tried using evil-winRM and was logged in with a shell.

Further enumeration

Finding user creds

Immediately after logging in I knew I had a privilege escalation path. Either of SeBackupPrivilege or SeRestorePrivilege can be abused for privilege escalation, but its nicer having both!

User.txt

Path to Power (Gaining Administrator Access)

Enumeration as User svc_backup

So much for the easy way to get the flag. with the SeBackupPrivilege I should have the ability to backup any file, but it looked like there was something limiting it. I did get a file notes.txt

So the "audit report" (root.txt) is encrypted. That would explain why it cannot be copied directly. I guess I have to privesc to the Administrator user first in order to decrypt it. Searching for SeBackupPrivilege led me to https://hackinparis.com/data/slides/2019/talks/HIP2019-Andrea_Pierini-Whoami_Priv_Show_Me_Your_Privileges_And_I_Will_Lead_You_To_System.pdf

Members of “Backup Operators” can logon locally on a Domain Controller and backup the NTDS.DIT, for ex. with: “wbadmin.exe” or “diskshadow.exe”

will try wbadmin.exe to backup files and try to backup to local share rather than trying to exfil later

created a samba share using impacket to copy over my loot https://pentestlab.blog/tag/diskshadow/

Unfortunately it wont' back up to a drive that is not formatted with NTFS, and wont backup to the same drive letter.

It took a bit of research and troubleshooting, but I found a workaround, in the form of using the network path for the local drive instead of the drive letter. Now I just had to restore my backup to a location I controlled and exfiltrate the file. I would also have to exfil the SYSTEM hive as well.

First I had to get the version identifier of the backup. It seemed like there was already a backup that had been made to 10.10.14.4\blackfieldA\ on 9/21/2020.

Next I saved each of the registry hives and downloaded all of the files. Unfortunately the SECURITY hive would not save, but I didn't really need it for getting the password hashes. Luckily exfiltrating files is very easy to do in an Evil-WinRM shell!

Getting a shell

Using Impacket's secretsdump.py I was able to dump the password hashes for all of the domain users (including the 300+ Blackfield123456 users!)

Root.txt

After collecting the flag, I went to verify the reason that I was unable to back up root.txt.

Using the cipher.exe command I was indeed able to see that the file was encrypted. The PowerShell script watcher.ps1 that I had seen earlier in the Administrator's documents folder when I logged in was the reason.

The script watcher.ps1 is the reason that root.txt was encrypted

Thanks to aas for something interesting or useful about this machine.

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