Skip to content
Fencer Intel
high 8.8

CVE-2026-126186 json

Active Storage: Possible arbitrary file read and remote code execution in Active Storage video previews, analysis and image processing

published 8d ago modified yesterday also EUVD-2026-122941 , GHSA-v924-7rp8-4mxh

cvss
8.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

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.

Patch / fix

  • rubygems activestorage 8.0.5.2, 8.1.4.1

Is CVE-2026-126186 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-126186 updated cvss 8.8

activestorage: Active Storage: Remote code execution via unsafe file extension handling in media processing

  • Red Hat 3scale API Management Platform 2 3scale-amp2/zync-rhel9, 3scale-amp2/system-rhel8, 3scale-amp2/system-rhel9
    affected: workaround, no fix available

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
GitHub 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
rubygems activestorage
>=8.1.0.beta1, <8.1.4.1
<8.0.5.2
8.1.4.1
8.0.5.2

Affected products

  • rails rails

Classification

Weakness
  • CWE-646 Reliance on File Name or Extension of Externally-Supplied File
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of rails/rails published their own advisory on GitHub. Reviewed sources take precedence over it.