CVE-2026-44738: Grav CMS Twig Sandbox Information Disclosure via Config::toArray()

Grav CMS is a widely deployed file-based Web platform that utilizes the Twig templating engine for rendering content and managing display logic. To secure its templating system and protect underlying architecture, Grav implements a Twig sandbox mechanism. This sandbox is purposefully designed to restrict the functions, methods, and properties available to standard content editors, preventing unauthorized code execution and limiting access to sensitive PHP environments.

CVE-2026-44738 represents a critical configuration failure within this sandbox implementation. The vulnerability permits authenticated users possessing the admin.pages role to completely bypass intended data access restrictions. This role is a standard assignment for content contributors, meaning the exploit can be executed by lower-privileged accounts to compromise the entire instance infrastructure.

The core issue is formally classified under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor. By abusing an overly permissive sandbox configuration, an attacker forces the application to render the complete, merged site configuration directly into the HTML output of a webpage. This configuration dataset invariably contains the sensitive secrets required for system operation and third-party service integrations.

The vulnerability originates from the specific configuration of the Twig sandbox allow-list within the Grav CMS core architecture. The sandbox is strictly responsible for filtering the methods that can be invoked on objects passed into the Twig rendering context. The Grav\Common\Config\Config object, which structurally holds the entire state of the application's configuration, is exposed to the Twig environment to allow frontend designers to access safe, operational configuration variables.

However, the sandbox allow-list incorrectly granted access to the toArray() method belonging to this Config object. The toArray() method is a utility function that recursively iterates through the entire configuration tree. It operates by converting the underlying structured object data into a flat, standard PHP array. This recursive conversion includes both public-facing system settings and deeply nested internal security parameters.

When an attacker calls this specific method from within a Twig template, the templating engine processes the request without triggering any sandbox security exceptions. The resulting complete configuration array is subsequently passed to the rendering engine. The rendering engine serializes and embeds this raw array data directly into the final HTML output of the page. The technical failure lies entirely in the overly broad permissions granted to the Config object within the restrictive sandbox context.

Exploitation of CVE-2026-44738 mandates that the attacker possesses an active, authenticated account on the target Grav CMS instance. The account must be provisioned with the admin.pages role, which grants the necessary permissions to create or edit page content. Once authenticated, the attacker accesses the Grav Admin panel and navigates to the standard page management interface.

The attacker crafts a malicious Twig payload and directly injects it into the Markdown or HTML body of a targeted page. The foundational payload consists of the template tags {{ config.toArray() }}. Depending on the target environment and specific rendering constraints, the attacker typically chains this method call with formatting filters. Payloads such as {{ config.toArray()|json_encode }} or {{ config.toArray()|print_r }} ensure the resulting output is cleanly structured and easily parsed from the rendered page source.

After saving the modified page, the attacker views the public-facing URL or utilizes the administrative preview function provided by the CMS. The Grav rendering engine parses the Twig tags, successfully bypasses the sandbox via the explicitly allowed toArray() method, and triggers the configuration dump. The attacker then simply accesses the HTTP response body and scrapes the HTML source code to extract the serialized configuration secrets.

The security impact of CVE-2026-44738 is classified as high severity, carrying a CVSS v3.1 base score of 7.7. The unauthorized disclosure of the merged system configuration provides an attacker with the cryptographic keys and authentication tokens required to compromise the entire infrastructure supporting the Grav installation. This significantly alters the scope of the initial compromise, extending the threat horizon from a single web application to multiple integrated external services.

The exposed dataset typically includes core system secrets, such as framework security salts and internal encryption keys. Attackers leverage these specific values to forge administrative sessions or locally decrypt other sensitive data stored within the file system. Furthermore, the configuration intrinsically holds highly sensitive third-party plugin parameters necessary for site operations.

Attackers can immediately harvest cleartext SMTP server credentials, AWS Access Key IDs and Secret Access Keys, OAuth client secrets, and various administrative API tokens for external service providers. If the Grav instance is configured to connect to external databases via specific data plugins, the connection strings and associated authentication credentials are also fully exposed. This comprehensive data leak enables attackers to rapidly escalate privileges, pivot to adjacent internal networks, or compromise third-party service accounts.

The vendor explicitly addressed the root cause of CVE-2026-44738 in Grav version 2.0.0-rc.2. The primary and most effective mitigation strategy is an immediate upgrade to this patched release or any subsequent stable version. System administrators must verify the active software version via the Grav administrative dashboard or by utilizing the bin/gpm command-line interface tool.

The underlying code remediation involves modifying the core Twig sandbox security policy to explicitly remove the toArray() method from the allow-list governing the Config object. By categorically denying access to this specific recursive dump function, the templating engine raises a fatal sandbox security exception when the payload execution is attempted. This directly neutralizes the attacker's ability to extract the configuration state.

// Conceptual representation of the required sandbox policy modification
$policy = new \Twig\Sandbox\SecurityPolicy(
    $allowedTags, 
    $allowedFilters, 
    $allowedMethods, 
    $allowedProperties, 
    $allowedFunctions
);
 
// The patch specifically removes 'toArray' from the allowed methods for the Config class
// Vulnerable State: $allowedMethods = ['Grav\Common\Config\Config' => ['get', 'toArray', ...]];
// Patched State:    $allowedMethods = ['Grav\Common\Config\Config' => ['get', ...]];

If immediate patching is operationally impossible, administrators must strictly audit all user accounts holding the admin.pages role. Revoking this specific role from untrusted or unverified accounts effectively eliminates the primary exploitation prerequisite. Following the application of the patch, organizations must immediately cycle and rotate all system secrets, application passwords, and third-party API keys that were present in the configuration prior to remediation.