Critical RCE Vulnerability CVE-2026-66066 Affects Ruby on Rails Active Storage with libvips
A critical vulnerability CVE-2026-66066 has been discovered in the popular web application framework Ruby on Rails. The issue, nicknamed KindaRails2Shell by some researchers, affects deployments that rely on Active Storage combined with the libvips image processing engine.
The flaw originates from unsafe operations permitted in the libvips dependency library. By uploading a specially crafted file, an unauthenticated attacker can read arbitrary files on the server. This capability may expose process environment variables, secret keys, and authentication credentials for external services.
Once sensitive data is obtained, attackers can leverage it to execute arbitrary code remotely or chain the access into broader compromise. The vulnerability is difficult to mitigate with web application firewalls, making prompt patching the primary defense.
The CVSS v4.0 base score is 9.5, placing the issue in the highest severity category of Critical. JPCERT/CC has published an advisory recommending immediate updates to affected Ruby on Rails installations.
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