---
id: "GHSA-f3w6-w445-fwh9"
page: "https://infrastack.ai/live/GHSA-f3w6-w445-fwh9"
kind: "vulnerability"
aliases: ["GHSA-f3w6-w445-fwh9"]
title: "Possible arbitrary file write and read in Active Storage image analysis"
severity: "critical"
cvss: 9.8
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "activestorage", "fixed": ["8.1.4.1"], "affected": ">= 8.1, < 8.1.4.1", "ecosystem": "rubygems"}, {"name": "activestorage", "fixed": ["8.0.5.2"], "affected": "< 8.0.5.2", "ecosystem": "rubygems"}]
ecosystems: ["rubygems"]
tags: ["activestorage", "cwe-1188", "imagemagick", "mini_magick", "package", "rails", "self-hosted"]
not_affected_if: ["unpatched-versions-excluded", "uploads-trusted-only", "variant-processor-not-mini-magick"]
published_at: "2026-11-04T03:09:06+00:00"
first_seen_at: "2026-11-09T22:53:28+00:00"
updated_at: "2026-11-09T22:54:06+00:00"
sources: [{"source": "ghsa-repo", "url": "https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9", "first_seen_at": "2026-11-09T22:53:28+00:00"}]
exploit_sources: []
---

# Possible arbitrary file write and read in Active Storage image analysis

Link for people: https://infrastack.ai/live/GHSA-f3w6-w445-fwh9 (this .md is for agents)

Rails Active Storage passes uploaded images to ImageMagick without restricting its coders, so a crafted file can make ImageMagick write arbitrary files on the server. When attachments use the Disk service, the attacker can also read files the application process can read, such as secret_key_base and credentials.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- rubygems:activestorage affected >= 8.1, < 8.1.4.1 fixed 8.1.4.1
- rubygems:activestorage affected < 8.0.5.2 fixed 8.0.5.2

## How to check

- Check the `activestorage` version in `Gemfile.lock` against the affected ranges: `>= 8.1, < 8.1.4.1` and `< 8.0.5.2`.
- Check whether `config.active_storage.variant_processor` is `:mini_magick` (the default on `load_defaults 6.1` or earlier).
- Check whether the app accepts file uploads from untrusted users.

## Fix

- `activestorage` 8.1.x: upgrade to `8.1.4.1`
- `activestorage` 8.0.x: upgrade to `8.0.5.2`
- Patches for teams that cannot upgrade at once are linked in the advisory (commits for 8.1 and 8.0).

## Timeline

- 2026-11-09T22:53:28+00:00 ghsa-repo https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9

## Documents

- [advisory] Vendor advisory: github.com https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9
- [discussion] @feross: We shipped a free Certified Patch for the 9.8 Rails Active Storage flaw. It clos https://x.com/feross/status/2118863523702874471
- [mentions] Critical Rails Flaw Lets Attackers Write Server Files via Crafted ImageMagick Uploads https://thehackernews.com/2026/11/critical-rails-flaw-lets-attackers.html

## From the sources

### Impact
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 `secret_key_base` and credentials for external systems, which may in turn allow escalation to remote code execution or lateral movement to those systems.

### Details
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 to us, but we do not assume it is the only one that exists.

The fixed versions ship an ImageMagick security policy and prepend its directory to `MAGICK_CONFIGURE_PATH` through `MiniMagick.cli_env`, so every ImageMagick process that MiniMagick spawns applies it. The policy denies the `MSL` scripting coder, the coders that read or delete files other than the image, fetch remote or local references, or display to a screen, every coder backed by Ghostscript together with the `gs` delegate, and `@filename` indirection. ImageMagick applies every `policy.xml` on its search path, so the shipped policy adds to the host's policy rather than replacing it. The policy applies to every ImageMagick command that MiniMagick runs, not only those of Active Storage. See the `activestorage` CHANGELOG and "ImageMagick Security Policy" in the Active Storage guide.

### Affected applications
An application is affected if it meets all of these requirements:
- Uses ImageMagick for Active Storage image processing. This is `config.active_storage.variant_processor = :mini_magick`, which is the default for applications on `load_defaults 6.1` or earlier.
- Runs ImageMagick under a security policy that does not already deny the coders involved. The policies that Debian and Ubuntu package do not.
- Allows file uploads from untrusted users.

### Mitigation
- Upgrade to a fixed version of `activestorage`.
- An application whose variant processor is `:mini_magick` must use mini_magick `>= 5.1`, which applying the policy requires. With an older mini_magick, such an application raises an exception during boot.
- An application that renders PostScript or PDF through ImageMagick must re-allow the `gs` delegate and the coders it uses in the host's `policy.xml`.
- An application that replaces `MiniMagick.cli_env` after boot, clears the environment with `MiniMagick.cli_prefix`, or installs its own `MiniMagick::Shell` does not receive the shipped policy and must carry its rules in ImageMagick's system policy. GraphicsMagick does not read ImageMagick policies.
- If attachments are stored with the Disk service, change `secret_key_base` and every secret readable by the application process, including the master key and everything `config/credentials.yml.enc` holds, storage and database credentials, and third-party tokens. Do not retain an exposed secret as a fallback.

### Workarounds
Copy the rules of the policy that the fixed versions ship, `activestorage/lib/active_storage/image_magick/policy.xml`, into ImageMagick's system policy, for example `/etc/ImageMagick-7/policy.xml`. At a minimum, deny the `MSL` coder, the Ghostscript coders, and the `gs` delegate:

```xml
<policy domain="coder" rights="none" pattern="MSL"/>
<policy domain="delegate" rights="none" pattern="gs"/>
<policy domain="coder" rights="none" pattern="{PS,PS2,PS3,EPS,EPS2,EPS3,EPI,EPSF,EPSI,EPT,EPT2,EPT3,PDF,AI,EPDF,PDFA,POCKETMOD,XPS,PCL}"/>
```

### Releases
The fixed releases are available at the normal locations.

Patches for those who cannot upgrade at once:
- 8.1: https://github.com/rails/rails/commit/468aa9a93fc98f5476b6821770f4ccfcb7f7d328
- 8.0: https://github.com/rails/rails/commit/ea8c40121ce53a3d0255cd4eb6d13bfe3bc01776

### Versions affected
- activestorage < 8.0.5.2
- activestorage >= 8.1, < 8.1.4.1

### Credit
This issue was responsibly reported by HackerOne researcher [ryotak](https://hackerone.com/ryotak).

### References
- ImageMagick [security policy](https://imagemagick.org/security-policy/)

---

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