Grav is a file-based Web platform. Prior to 1.7.53 and 2.0.0-rc.8, Grav allows an unauthenticated visitor to exhaust server memory and CPU by requesting image derivatives with oversized dimensions through URL query image actions such as forceResize in Grav::fallbackUrl, which passes request parameters to ImageMedium magic actions without a dimension or pixel ceiling. This issue is fixed in versions 1.7.53 and 2.0.0-rc.8.

Affected: Packagist: getgrav/grav

### Summary An unauthenticated visitor exhausts server memory and CPU by requesting an image with oversized resize dimensions. One request drives a worker to several gigabytes of RAM and tens of seconds of CPU. A few concurrent requests take the host down.

### Details `Grav::fallbackUrl()` (system/src/Grav/Common/Grav.php:800-804) loops over every query parameter and, when the name matches `ImageMedium::$magic_actions`, calls that method on the medium with the comma-split value as arguments:

```php foreach ($uri->query(null, true) as $action => $params) { if (in_array($action, ImageMedium::$magic_actions, true)) { call_user_func_array([&$medium, $action], explode(',', $params)); } } ```

`forceResize` runs with `force=true`, so it sets the output size to the attacker's values with no clamp against the source or any ceiling. The `getgrav/image` GD adapter then calls `imagecreatetruecolor($w, $h)`. libgd allocates that buffer outside PHP's `emalloc`, so `memory_limit` does not cap it. Grav exposes no `system.images.max_width`/`max_height` setting.

### PoC Any page that serves an image works. With a 200x150 source image:

``` GET /home/test.png?forceResize=20000,20000 ```

Measured on PHP 8.4.21 with `memory_limit=128M`:

- peak worker RSS 3,109 MB - 21.9 s CPU - HTTP 200, 1.6 MB response

`8000x8000` already needs ~244 MB. The cache key includes the dimensions, so varying them forces fresh work on every request.

### Impact Unauthenticated denial of service…