KindaRails2Shell: CVE-2026-66066, Critical Arbitrary File Read and Possible Remote Code Execution in Ruby on Rails

OverviewOn 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 v…