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Support

Summary

We scan the machine using nmap and find that SMB and LDAP are running. We are able to list SMB shares and download all the files from the support-tools share without providing credentials. One of the files downloaded is a ZIP file containing a .Net executable called UserInfo.exe. We decompile the program with AvaloniaILSpy (which is a port of ILSpy to Linux/MacOS) and find an encrypted password. The encryption is basic and the decryption logic is already present in the code, so the password is easy to decrypt. We continue looking at the code and find an LDAP connection is made through a user called ldap and the decrypted password.

Using ldapsearch, we dump the LDAP user data and find the password for the support user in its info field. We connect using evil-winrm and get the user.txt flag.

Now that we have a shell, we scan the machine using SharpHound and BloodHound. We figure out that the SHARED SUPPORT [email protected] group has the GenericAll permission on DC.SUPPORT.HTB and our user, support is part of that group.

Searching for ways to exploit the GenericAll permission finds Kerberos Resource-based Constrained Delegation: Computer Object Takeover. Following the guide, we 1) create a fake computer object (no admin required) and 2) update the target computer object to enable the fake computer to impersonate and authenticate any domain user that can then access the target system. The second step is possible because we have the WRITE privilege (from GenericAll) on the target machine. Instead of following the guide to create the ticket (it uses a Window-only tool), we use impacket's getST.py. This gives us a Kerberos ticket with the ability to impersonate the Administrator user. Finally, we use wmiexec.py with the ticket to get an interactive shell on the box as Administrator and get the root.txt flag.

Enumeration

Nmap

First, let's scan for open ports using nmap. We can quickly scan for open ports and store them in a variable: ports=$(nmap -Pn -p- --min-rate=1000 -T4 10.129.227.255 | grep '^[0-9]' | cut -d '/' -f 1 | tr '\n' ',' | sed s/,$//). Then, we can scan those specific ports in depth by running nmap's built-in scripts: nmap -Pn -p$ports -sC -sV 10.129.227.255. We need to use -Pn with this box since it is blocking nmap's ping probes.

PORT      STATE SERVICE       VERSION
53/tcp    open  domain        Simple DNS Plus
88/tcp    open  kerberos-sec  Microsoft Windows Kerberos (server time: 2022-08-01 22:42:32Z)
135/tcp   open  msrpc         Microsoft Windows RPC
139/tcp   open  netbios-ssn   Microsoft Windows netbios-ssn
389/tcp   open  ldap          Microsoft Windows Active Directory LDAP (Domain: support.htb0., Site: Default-First-Site-Name)
445/tcp   open  microsoft-ds?
464/tcp   open  kpasswd5?
593/tcp   open  ncacn_http    Microsoft Windows RPC over HTTP 1.0
636/tcp   open  tcpwrapped
3269/tcp  open  tcpwrapped
5985/tcp  open  http          Microsoft HTTPAPI httpd 2.0 (SSDP/UPnP)
|_http-server-header: Microsoft-HTTPAPI/2.0
|_http-title: Not Found
9389/tcp  open  mc-nmf        .NET Message Framing
49664/tcp open  msrpc         Microsoft Windows RPC
49667/tcp open  msrpc         Microsoft Windows RPC
49670/tcp open  ncacn_http    Microsoft Windows RPC over HTTP 1.0
49674/tcp open  msrpc         Microsoft Windows RPC
49699/tcp open  msrpc         Microsoft Windows RPC
55397/tcp open  msrpc         Microsoft Windows RPC
Service Info: Host: DC; OS: Windows; CPE: cpe:/o:microsoft:windows

Host script results:
| smb2-time:
|   date: 2022-08-01T22:43:23
|_  start_date: N/A
|_clock-skew: -1s
| smb2-security-mode:
|   3.1.1:
|_    Message signing enabled and required

SMB (Ports 139 & 445)

Ports 139 and 445 are open so it looks like SMB is running.

We can try listing the shares (-L) without specifying a password (-N).

support-tools is interesting. Let's try to view the files from that share using an interactive shell:

It's a directory of different programs. We can download all these files to the current directory by running the following commands from this HackTricks page:

Alternatively, you can download one file by running get UserInfo.exe.zip.

Decompiling UserInfo.exe

Everything except UserInfo.exe.zip looks like a normal program. When unzipping UserInfo.exe.zip we see the following files:

Running file UserInfo.exe tells us that this is a PE32 executable (console) Intel 80386 Mono/.Net assembly, for MS Windows. I am familiar with reversing using Ghidra, but it is not the right tool to reverse .Net binaries. Searching for ".net debugger" finds dnSpy, but the repository is archived and hasn't been updated for about 2 years. I also find ILSpy which seems to be more regularly updated. This article from ndepend compares the available decompilers. I'm going to use ILSpy since the article calls it "the de-facto .NET Decompiler." ILSpy only supports Windows, but it has been ported to Linux in the form of AvaloniaILSpy. Download the latest release from the releases page and run it with ./ILSpy.

We open the UserInfo.exe binary in ILSpy and quite quickly we find the UserInfo.Services.Protected class, which contains and encrypted password and a method to decrypt it already written for us:

UserInfo.Services.Protected class (in text form):

Let's quickly write this in Python (since that is faster than getting C# code running):

This prints out nvEfEK16^1aM4$e7AclUf8x$tRWxPWO1%lmz.

Additionally, in ILSpy, we see a class called UserInfo.Services.LdapQuery.

After looking at it, we see that the constructor contains a username (ldap) and uses the decoded password to connect to LDAP on the machine.

LDAP

From the nmap scan and the UserInfo.exe, we see that LDAP is present. LDAP runs on ports 389, 636, 3268, and 3269. According to Wikipedia, "The Lightweight Directory Access Protocol is an open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed directory information services over an Internet Protocol network."

According to HackTricks, we can make sure our credentials work by trying to extract everything from the LDAP server by running ldapsearch -x -H ldap://<IP> -D '<DOMAIN>\<username>' -w '<password>' -b "DC=<1_SUBDOMAIN>,DC=<TLD>". Here are what the options in this command mean:

For our situation, this command is ldapsearch -x -H ldap://10.129.227.255 -D 'support\ldap' -w 'nvEfEK16^1aM4$e7AclUf8x$tRWxPWO1%lmz' -b "DC=support,DC=htb". This outputs 5824 lines of output. So, we captured it all into ldap_dump.txt.

We can get only information about users by adding CN=Users to the command like so (command from HackTricks): ldapsearch -x -H ldap://10.129.227.255 -D 'support\ldap' -w 'nvEfEK16^1aM4$e7AclUf8x$tRWxPWO1%lmz' -b "CN=Users,DC=support,DC=htb". Tip: Pipe the output of that command to xclip -selection clipboard to copy it to your clipboard automatically. Output is located at ldap_users.txt. After looking through this file, we see the support user has the info field set to Ironside47pleasure40Watchful, which is weird.

Foothold

The piece of information we found is the support user's password. WinRM runs on port 5985, which is open. We can connect using evil-winrm by running evil-winrm -u support -p Ironside47pleasure40Watchful -i 10.129.227.255, which works.

Now, just run cat C:\Users\support\Desktop\user.txt to get the user.txt flag.

Privilege Escalation

Let's scan the machine using BloodHound: "BloodHound is a single page Javascript web application, built on top of Linkurious, compiled with Electron, with a Neo4j database fed by a C# data collector. BloodHound uses graph theory to reveal the hidden and often unintended relationships within an Active Directory or Azure environment. Attackers can use BloodHound to easily identify highly complex attack paths that would otherwise be impossible to quickly identify."

BloodHound only analyzes data though. We need to use SharpHound (download) to collect data. There are other data collectors but SharpHound is the only officially support collector.

Upload SharpHound.exe and run it:

To get BloodHound setup, you can follow this guide. Then, just download the zip file (20220801170020_BloodHound.zip) from the machine and drag and drop it onto the BloodHound interface. Then, on the Analysis tab, choose "Shortest Paths to High Value Targets":

Right click the DC.SUPPORT.HTB machine and choose "Shortest Paths to Here":

The SHARED SUPPORT [email protected] group has the GenericAll permission on DC.SUPPORT.HTB. If we right click that group, we will see that the support user we have access to is a member of the group. So, we have the GenericAll permission.

Searching for "genericall active directory" finds this page, which explains that "if you have GenericAll/GenericWrite/Write on a Computer object, you can pull Kerberos Resource-based Constrained Delegation: Computer Object Takeover off.

We need the following PowerShell modules to follow the guide: PowerView.ps1 (GitHub repo) and Powermad.ps1 (GitHub repo). Download them and then upload them to the box using evil-winrm's upload command. Load them by running the following commands:

The first step is to create a new computer object for our fake computer, FAKE01. This is the computer that will be trusted by our target computer dc.support.htb later on.

Output:

Get the newly created computer SID with Get-DomainComputer fake01:

The SID is S-1-5-21-1677581083-3380853377-188903654-5601.

Next, create a new raw security descriptor for the FAKE01 computer principal:

After that, apply the security descriptor bytes to the target dc.support.htb machine by running Get-DomainComputer dc | Set-DomainObject -Set @{'msds-allowedtoactonbehalfofotheridentity'=$SDBytes} -Verbose:

To get a Kerberos ticket, the guide uses Rubeus, which only runs on Windows and seems difficult to set up. Searching for "impacket get kerberos ticket to impersonate user" finds impacket's getST.py:

Now we have the Kerberos ticket. Looking at the tools available in impacket shows "wmiexec.py: A semi-interactive shell, used through Windows Management Instrumentation. It does not require to install any service/agent at the target server. Runs as Administrator. Highly stealthy." It also has an option to use a Kerberos ticket through the KRB5CCNAME environment variable. It looks like smbexec.py is popular and would work as well.

So, let's run the following to get a shell:

Initially, I got the error [-] [Errno Connection error (dc.support.htb:445)] [Errno -3] Temporary failure in name resolution. So, I added dc.support.htb and support.htb to the /etc/hosts file. After that, the command worked!

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