Remote shell execution vulnerability when applying commands from user input

Impact

When using the #apply method from image_processing to apply a series of operations that are coming from unsanitized user input, this allows the attacker to execute shell commands:

ImageProcessing::Vips.apply({ system: "echo EXECUTED" })
#>> EXECUTED

This method is called internally by Active Storage variants, so Active Storage is vulnerable as well.

Patches

The vulnerability has been fixed in version 1.12.2 of image_processing.

Workarounds

If you’re processing based on user input, it’s highly recommended that you always sanitize the user input, by allowing only a constrained set of operations. For example:

operations = params[:operations]
  .map { |operation| [operation[:name], *operation[:value]] }
  .select { |name, *| name.to_s.include? %w[resize_to_limit strip ...] } # sanitization

ImageProcessing::Vips.apply(operations)