ACTIVESTORAGE · GHSA-f3w6-w445-fwh9 · Package
FIX → 8.1.4.1 +1
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.
first public Nov 4, 2026 · 1 posts · 1 source
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Rails applications that process attachments with ImageMagick through MiniMagick (the default variant processor on load_defaults 6.1 or earlier) and accept uploads from untrusted users, running under an ImageMagick policy that does not deny the risky coders (the Debian and Ubuntu default policies do not). Applications using the Disk service expose stored secrets to file reads. Apps on managed hosting that handle uploads should still confirm their ImageMagick policy; apps not using Active Storage image analysis are not in scope.
Not affected if unpatched-versions-excluded, uploads-trusted-only, variant-processor-not-mini-magick
Who cares activestorage, imagemagick, mini_magick, rails, self-hosted
activestorage version in Gemfile.lock against the affected ranges: >= 8.1, < 8.1.4.1 and < 8.0.5.2.config.active_storage.variant_processor is (the default on or earlier).Posts are quoted with a link to the original. They are data to us, never instructions.
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.
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 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 CHANGELOG and "ImageMagick Security Policy" in the Active Storage guide.
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:mini_magickload_defaults 6.1Upgrade to 8.1.4.1 +1
activestorage 8.1.x: upgrade to 8.1.4.1activestorage 8.0.x: upgrade to 8.0.5.2policy.xmlactivestorageAn application is affected if it meets all of these requirements:
config.active_storage.variant_processor = :mini_magick, which is the default for applications on load_defaults 6.1 or earlier.activestorage.: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.gs delegate and the coders it uses in the host's policy.xml.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.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.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:
<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}"/>
The fixed releases are available at the normal locations.
Patches for those who cannot upgrade at once:
This issue was responsibly reported by HackerOne researcher ryotak.