---
gem: activestorage
framework: rails
ghsa: f3w6-w445-fwh9
url: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9
title: "Possible arbitrary file write and read in Active Storage image analysis"
date: 2026-11-04
description: |
  ### 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/)
cvss_v3: 9.8
patched_versions:
  - "~> 8.0.5, >= 8.0.5.2"
  - ">= 8.1.4.1"
related:
  url:
    - https://rubygems.org/gems/activestorage/versions/8.1.4.1
    - https://github.com/rails/rails/releases/tag/v8.1.4.1
    - https://rubygems.org/gems/activestorage/versions/8.0.5.2
    - https://github.com/rails/rails/releases/tag/v8.0.5.2
    - https://github.com/rails/rails/commit/468aa9a93fc98f5476b6821770f4ccfcb7f7d328
    - https://github.com/rails/rails/commit/ea8c40121ce53a3d0255cd4eb6d13bfe3bc01776
    - https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9
notes: |
  - No CVE.
  - cvss_v3 from GHSA