Overview
On July 29, 2026, the Ruby on Rails project published a security advisory for CVE-2026-66066, a critical vulnerability affecting Active Storage image processing when used in conjunction with the libvips image processing library. The vulnerability has a CVSSv4 score of 9.5 and is classified as Initialization of a Resource with an Insecure Default (CWE-1188). An unauthenticated attacker may be able to leverage CVE-2026-66066 and read files accessible to the Rails application process, potentially exposing secrets that could enable remote code execution (RCE) or access to connected systems.
An application is affected when it uses libvips for Active Storage image processing and accepts image uploads from untrusted users. Rails notes that generating image variants is not a separate requirement for exposure. Vips is the default Active Storage variant processor for applications configured with Rails 7.0 or later defaults. According to Ethiack, only the Vips processor is affected; applications using Magick are not affected through the reported vector.
As of July 30, 2026, Rapid7 is not aware of exploitation in the wild. Ethiack and GMO Flatt Security, who independently reported the vulnerability, have withheld proof-of-concept code and details of the full attack chain. Public code claiming to exploit CVE-2026-66066 exists, but it is unclear how closely it corresponds to the full attack chain reported privately to Rails. According to the Rails Security Announcement, additional details will be disclosed no later than August 28, 2026. Rapid7 recommends remediating affected applications on an urgent basis, outside of normal patch cycles.
Technical overview
libvips uses operations to load and save image formats, including operations backed by third-party libraries. Some are marked "unfuzzed" or "untrusted" because they are unsafe for untrusted content. According to Rails, Active Storage did not disable these operations before processing user-supplied files, which may allow a crafted upload to trigger an unsafe operation and disclose files readable by the application.
The Rails patch that remediates CVE-2026-66066, disables untrusted operations during Active Storage initialization. When ruby-vips is installed, patched versions prevent the application from starting if ruby-vips or libvips is too old to support that protection.
Mitigation guidance
Organizations running affected Ruby on Rails applications should upgrade to a fixed Active Storage release and ensure libvips is 8.13 or later. Updating Rails or Active Storage alone is not sufficient when an older libvips version is installed.
The Rails advisory identifies patched Active Storage releases 7.2.3.2, 8.0.5.1, and 8.1.3.1. The corresponding Rails releases are:
Rails branch | Affected versions | Fixed version |
|---|---|---|
Rails 7.x | 7.0.0 through 7.2.3.1 | 7.2.3.2 |
Rails 8.0.x | 8.0.0 through 8.0.5 | 8.0.5.1 |
Rails 8.1.x | 8.1.0 through 8.1.3 | 8.1.3.1 |
Ethiack reports that Rails 6.0.0 through 6.1.7.10 may also be affected when Active Storage is configured to use Vips; Rails 6.x does not use Vips by default. Rails has not published a fixed 6.x release, so affected Rails 6.x applications should migrate to a supported fixed branch or apply the applicable workaround below.
When ruby-vips is installed, organizations should ensure it is 2.2.1 or later. Rails advises affected organizations to replace secret_key_base and other secrets accessible to the application process, including the Rails master key and the credentials it decrypts, storage service credentials, database credentials, and third-party service tokens or keys. Replacing secret_key_base expires active sessions and affects encrypted and signed cookies, signed global IDs, and Active Storage URLs.
As a temporary workaround on libvips 8.13 or later, organizations can set VIPS_BLOCK_UNTRUSTED or, with ruby-vips 2.2.1 or later, call Vips.block_untrusted(true) from an initializer. For libvips versions earlier than 8.13, Rails states that the only workaround is to remove the libvips dependency.
For the latest mitigation guidance, please refer to the Ruby on Rails security advisory.
Rapid7 customers
Exposure Command, InsightVM, and Nexpose
Exposure Command, InsightVM, and Nexpose customers can assess exposure to CVE-2026-66066 with vulnerability checks expected to be available in the July 31 content release.
Updates
July 30, 2026: Initial publication.