Details

1. All Imagick supported Fileformats are served without filtering

The Thumbnail endpoint does not check against any filters what file formats should be served. We can transcode the image in all formats imagemagick supports. With that we can create Files that are much larger in filesize than the original. For example we can create a .txt file for all thumbnails, and we get the text representation of the image.

We can demonstrate that with the pimcore demo:

This Thumbnail is found on the Frontend: https://demo.pimcore.fun/Sample%20Content/Background%20Images/317/image-thumb__317__standardTeaser/11.8c64bd89.avif (12kb Filesize)

We can generate a text representation by simply changing the file extension: https://demo.pimcore.fun/Sample%20Content/Background%20Images/317/image-thumb__317__standardTeaser/11.8c64bd89.txt (4.59mb Filesize)

Other (large) fileformats we tested: ftxt, dip, bmp, bmp3, bmp2, farbfeld, cmyk, cmyka, ycbcr, ycbcra and many more (just check imagemagick supported formats)

With that we can fill the available space of a server really easy.

With formats like yaml or json we can also expose exif data of the original image file - could be a concern with gps data in user uploaded images.

TLDR

• we can generate all imagemagick supported formats with all thumbnail configs
• all configs were the format is set to "auto (Web-optimized)" are vulnerable
• private (exif) data can be exposed.
• We can flood the the server with a bunch of files that are a multiple magnitudes of the original thumbnail size (see txt example), for all thumbnail configs, with every image that we find (scriptable)

Proposed Solution

Implement a list of allowed formats that the developer can modify if needed, if a file is requested in another format than listed, pimcore should return either "/bundles/pimcoreadmin/img/filetype-not-supported.svg" or a 404.

pimcore:
    thumbnails:
    	allowed_formats: ['jpg', 'png', 'avif', 'webp', 'gif']

For non-maintained Pimcore versions (<11), the webserver config could be used to only serve files that should be allowed.

2. Non Web optimized file formats (ORIGINAL, JPG, PNG) creates duplicated files on Server

With Thumbnail config that are configured to serve non web optimized file formats (such as ORIGINAL, jpg, png, print, etc) we can create files with arbitrary file formats that are saved to disk.