Rails Active Storage prior 8.0.5.2/8.1.4.1 Media Analysis ActiveStorage::Blob#open unrestricted upload

Summaryinfo

A vulnerability was found in Rails Active Storage. It has been rated as critical. Impacted is the function ActiveStorage::Blob#open of the component Media Analysis. The manipulation leads to unrestricted upload. This vulnerability is referenced as CVE-2026-126186. Remote exploitation of the attack is possible. No exploit is available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Rails Active Storage. This issue affects the function ActiveStorage::Blob#open of the component Media Analysis. The manipulation with an unknown input leads to a unrestricted upload vulnerability. Using CWE to declare the problem leads to CWE-434. The product allows the upload or transfer of dangerous file types that are automatically processed within its environment. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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 ffmpeg.org do. Other decoders that FFmpeg or ImageMagick select from the extension may be reachable without AviSynth. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-126186 since 11/10/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1608.002 for this issue.

Upgrading to version 8.0.5.2 or 8.1.4.1 eliminates this vulnerability.

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• Rails

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• Active Storage

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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