CyberSecBulletin
CVE-2026-66066NVD status: Awaiting Analysis

rails: Initialization of a Resource with an Insecure Default

Published Updated By the CyberSecBulletin desk

CVE-2026-66066 is a critical-severity initialization of a resource with an insecure default vulnerability in rails, with a CVSS 4.0 base score of 9.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected rails versions: < 7.2.3.2; >= 8.0.0.beta1, < 8.0.5.1; >= 8.1.0.beta1, < 8.1.3.1. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 32.9% chance of exploitation within 30 days, which is in the top 1.62% of all scored CVEs.

Patch this week

Critical severity: a successful attack would have severe impact.

What to do

  1. Check which version of rails you run against the affected versions below, and install the vendor's latest release.
  2. Read the advisory on github.com for workarounds and exact fixed builds.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
Railsrails< 7.2.3.2; >= 8.0.0.beta1, < 8.0.5.1; >= 8.1.0.beta1, < 8.1.3.1Not stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Attack requirements
PresentThe target must be in a specific state or configuration for the attack to work.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Confidentiality (vulnerable system)
HighSerious loss of confidentiality on the vulnerable system.
Integrity (vulnerable system)
HighSerious loss of integrity on the vulnerable system.
Availability (vulnerable system)
HighSerious loss of availability on the vulnerable system.
Confidentiality (other systems)
HighSerious loss of confidentiality on systems beyond the vulnerable one.
Integrity (other systems)
HighSerious loss of integrity on systems beyond the vulnerable one.
Availability (other systems)
HighSerious loss of availability on systems beyond the vulnerable one.

Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. Scored by CNA (github.com).

Official description

Action Pack is a framework for handling and responding to web requests. In versions prior to 7.2.3.2, 8.0.5.1 and 8.1.3.1, Active Storage does not disable libvips operations marked unsafe for untrusted content, allowing a crafted upload to invoke such an operation. Consuming applications are affected when configured to use libvips and accept image uploads from untrusted users. An unauthenticated attacker may exploit this behavior to read arbitrary files accessible to the Rails process, including environment variables and application secrets. Exposure of credentials such as secret_key_base or external-service tokens may enable remote code execution or lateral movement. This issue has been fixed in versions 7.2.3.2, 8.0.5.1 and 8.1.3.1.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Initialization of a Resource with an Insecure Default

The product initializes or sets a resource with a default that is intended to be changed by the product's installer, administrator, or maintainer, but the default is not secure.

More Initialization of a Resource with an Insecure Default vulnerabilities (CWE-1188)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in rails

All rails vulnerabilities

Recent Initialization of a Resource with an Insecure Default vulnerabilities

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