Active Storage makes it simple to upload and reference files in cloud services and attach those files to Active Record objects. Prior to 8.0.5.2 and from 8.1 until 8.1.4.1, Active Storage's ActiveStorage::Previewer::VideoPreviewer, ActiveStorage::Analyzer::VideoAnalyzer, and ActiveStorage::Analyzer::AudioAnalyzer pass uploaded blob contents to FFmpeg without restricting the demuxer. A direct upload can retain a client-declared video/ or audio/ content type for an HLS playlist. FFmpeg content probing selects the hls demuxer, which opens attacker-named file:// segments when the blob is previewed or analyzed. Applications that accept untrusted uploads and generate video previews or analyze video or audio attachments can disclose a local media file readable by the application process when the attacker knows its path. This issue is fixed in versions 8.0.5.2 and 8.1.4.1.

Active Storage makes it simple to upload and reference files in cloud services and attach those files to Active Record objects. Prior to 8.1.4.1 and 8.0.5.2, a Rails application that processes attachments with ImageMagick may allow an unauthenticated attacker to write arbitrary files on the server and, when attachments are stored with the Disk service, to read arbitrary files readable by the application process. Those files typically include secretkeybase and credentials for external systems, which may in turn allow escalation to remote code execution or lateral movement to those systems. ImageMagick selects a coder from the content of the file it is given, and some coders act on files named inside the image rather than on the image itself. Active Storage constrained none of ImageMagick's coders, and the ImageMagick analyzer runs when a file is attached, so an attacker who can upload a crafted file may be able to invoke one. Attaching the upload is sufficient; no variant, preview, or analyze call is required. One specific attack chain has been reported, but other attack chains may exist. An application is affected when it uses ImageMagick for Active Storage image processing through config.activestorage.variantprocessor = :minimagick, runs ImageMagick under a security policy that does not already deny the involved coders, and allows uploads from untrusted users. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

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!