Active Storage allows users to attach cloud and local files in Rails applications. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, Active Storage's DiskService#pathfor does not validate that the resolved filesystem path remains within the storage root directory. If a blob key containing path traversal sequences (e.g. ../) is used, it could allow reading, writing, or deleting arbitrary files on the server. Blob keys are expected to be trusted strings, but some applications could be passing user input as keys and would be affected. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Active Storage allowed transformation methods potentially unsafe

Active Storage attempts to prevent the use of potentially unsafe image transformation methods and parameters by default.

The default allowed list contains three methods allow for the circumvention of the safe defaults which enables potential command injection vulnerabilities in cases where arbitrary user supplied input is accepted as valid transformation methods or parameters.

Impact ------ This vulnerability impacts applications that use Active Storage with the imageprocessing processing gem in addition to minimagick as the image processor.

Vulnerable code will look something similar to this: <%= imagetag blob.variant(params[:t] => params[:v]) %>

Where the transformation method or its arguments are untrusted arbitrary input.

All users running an affected release should either upgrade or use one of the workarounds immediately.

Workarounds ----------- Consuming user supplied input for image transformation methods or their parameters is unsupported behavior and should be considered dangerous.

Strict validation of user supplied methods and parameters should be performed as well as having a strong ImageMagick security policy deployed.

Credits -------

Thank you lio346 for reporting this!