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GHSA-f3w6-w445-fwh9
activestorageactivestorageactivestorageImpact
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 onload_defaults 6.1or 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_magickmust 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
gsdelegate and the coders it uses in the host'spolicy.xml. - An application that replaces
MiniMagick.cli_envafter boot, clears the environment withMiniMagick.cli_prefix, or installs its ownMiniMagick::Shelldoes 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_baseand every secret readable by the application process, including the master key and everythingconfig/credentials.yml.encholds, 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:
<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.
References
- ImageMagick security policy
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
- CVE-2026-126082
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, 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, but other attack chains may exist. An application is affected when it uses ImageMagick for Active Storage image processing through config.active_storage.variant_processor = :mini_magick, runs ImageMagick under a security policy that does not already deny the involved coders, and allows uploads from untrusted users. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.
Alias, EPSS 0.74% - CVE-2026-122006
The activestorage gem before 8.1.4.1 for Ruby on Rails, when ImageMagick attachment processing occurs, can allow server read and write operations (e.g., reading secret_key_base) because the ImageMagick analyzer runs when a file is attached, and there is not an ImageMagick security policy to block unintended functionality.
Alias, EPSS 0.74% - EUVD-2026-116914Alias
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