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, ActiveStorage::Blob#open writes a blob to a tempfile whose name carries the extension of the uploaded filename, and hands that path to ffprobe (VideoAnalyzer, AudioAnalyzer), ffmpeg (VideoPreviewer) and ImageMagick (ImageAnalyzer, the :mini_magick variant processor). These tools select a decoder from the file extension when the content does not identify its own format, so an attacker who chooses the filename and declares the content type of an upload chooses which decoder processes it. An FFmpeg built with AviSynth support treats a file with the .avs extension as an AviSynth script and evaluates it, which could disclose files readable by the application process through the preview image, or load a native library the attacker has also uploaded, possibly leading to remote code execution in the FFmpeg process. ImageMagick selects its coders and delegates from the extension in the same way. An application is affected if it accepts uploads from untrusted users and analyzes video or audio attachments, generates video previews, or processes images with ImageMagick. The AviSynth attack additionally requires an FFmpeg built with --enable-avisynth and the AviSynthPlus runtime on the host. Upstream FFmpeg and the common Linux distribution and Homebrew packages do not enable it; the GPL builds distributed for Windows and Linux from…

Affected: RubyGems: activestorage

### Impact `ActiveStorage::Blob#open` writes a blob to a tempfile whose name carries the extension of the uploaded filename, and hands that path to `ffprobe` (`VideoAnalyzer`, `AudioAnalyzer`), `ffmpeg` (`VideoPreviewer`) and ImageMagick (`ImageAnalyzer`, the `:mini_magick` variant processor). These tools select a decoder from the file extension when the content does not identify its own format, so an attacker who chooses the filename and declares the content type of an upload chooses which decoder processes it. An FFmpeg built with AviSynth support treats a file with the `.avs` extension as an AviSynth script and evaluates it, which could disclose files readable by the application process through the preview image, or load a native library the attacker has also uploaded, possibly leading to remote code execution in the FFmpeg process. ImageMagick selects its coders and delegates from the extension in the same way.

### Details The fixed releases keep the uploaded extension on the tempfile only when Marcel maps that extension to the blob's recorded content type, and name the tempfile with no extension otherwise. A form upload whose Rack tempfile fails the same check is copied to a correctly named tempfile before processing. Files whose uploaded extension disagrees with their content type are still processed; the external tool detects their format from the content. The Active Storage CHANGELOG describes the change.

### Affected applications An application is affected if it m…

Affected: Ubuntu:Pro:16.04:LTS: rails, Ubuntu:Pro:18.04:LTS: rails, Ubuntu:Pro:20.04:LTS: rails, Ubuntu:Pro:22.04:LTS: rails, Ubuntu:24.04:LTS: rails, Ubuntu:26.10: rails, Ubuntu:26.04:LTS: rails

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, ActiveStorage::Blob#open writes a blob to a tempfile whose name carries the extension of the uploaded filename, and hands that path to ffprobe (VideoAnalyzer, AudioAnalyzer), ffmpeg (VideoPreviewer) and ImageMagick (ImageAnalyzer, the :mini_magick variant processor). These tools select a decoder from the file extension when the content does not identify its own format, so an attacker who chooses the filename and declares the content type of an upload chooses which decoder processes it. An FFmpeg built with AviSynth support treats a file with the .avs extension as an AviSynth script and evaluates it, which could disclose files readable by the application process through the preview image, or load a native library the attacker has also uploaded, possibly leading to remote code execution in the FFmpeg process. ImageMagick selects its coders and delegates from the extension in the same way. An application is affected if it accepts uploads from untrusted users and analyzes video or audio attachments, generates video previews, or processes images with ImageMagick. The AviSynth attack additionally requires an FFmpeg built with --enable-avisynth and the AviSynthPlus runtime on the host. Upstream FFmpeg and the common Linux distribution and Homebrew packages do not enable it; the GPL builds distributed for Windows and Linux from…

Ein Angreifer kann mehrere Schwachstellen in Ruby on Rails ausnutzen, um beliebigen Programmcode auszuführen, um einen Denial of Service Angriff durchzuführen, um Informationen offenzulegen, um Daten zu manipulieren, um falsche Informationen darzustellen, um einen Cross-Site Scripting Angriff durchzuführen und um Sicherheitsvorkehrungen zu umgehen.