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Action Pack: Possible arbitrary file read and remote code execution in Active Storage variant processing

Not in CISA KEVMetasploit moduleCVE-2026-66066CWE-1188

Not confirmed exploited. 2 of 8 rule sources name it; Cloudflare blocks by default.

Edge rules
2/8
Our test
No exploit yet
CVSS
9.5
EPSS
30.1% Top 2%
Posts, 14d
02026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts
Published
2026-07-30
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… More

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.

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Ask about CVE-2026-66066: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

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Severity, decoded

CVSS 4.0
Critical · 9.5 / 10

Exploitable over the network under specific conditions, with no privileges and no user interaction, leading to full loss of confidentiality, integrity and availability; other systems can also be hit (full loss of confidentiality, integrity and availability).

Over the internetNo login neededNo user actionWorks reliablySpreads beyond the appFull compromise
How the score is built11 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityNo built-in defences have to be bypassed; the attack works reliably.
    Low
  • Attack requirementsThe attack only works under specific conditions, such as a race or a particular setup.
    Present
  • Privileges requiredNo account or login is needed.
    None
  • User interactionNo one has to click or open anything; the attack works on its own.
    None
  • Confidentiality impact (vulnerable system)An attacker can read all data the affected component holds, or the most sensitive parts of it.
    High
  • Integrity impact (vulnerable system)An attacker can change any data or files the affected component protects.
    High
  • Availability impact (vulnerable system)An attacker can take the component down completely or keep it from serving anyone.
    High
  • Confidentiality impact (other systems)Other systems that rely on it can have all their data read.
    High
  • Integrity impact (other systems)Other systems that rely on it can have any data changed.
    High
  • Availability impact (other systems)Other systems that rely on it can be taken down.
    High
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
CISA's assessmentSSVC, from the CVE record
ExploitationProof of concept

Public exploit code or a detailed write-up exists, but CISA has not seen attacks.

AutomatableYes

Attackers can script the attack end to end and hit many targets at once.

Technical impactTotal

A successful attack gives full control over the affected software or all of its data.

Public exploits

1 found
1 Metasploit0 Exploit-DB0 Scanner template0 GitHub PoCs

Links are to third-party code: never run it outside an isolated lab.

Timeline

  1. 2026-07-29
    Metasploit module published
    Ruby on Rails Active Storage Vips Arbitrary File Read and Remote Code Execution
  2. 2026-07-30
    CVE published
    CVE List
  3. 2026-08-04
    Cloudflare rule names it
    Earliest entry we can see is an update
  4. 2026-09-16
    F5 ships a rule
    Ruby on Rails "Active Storage" Arbitrary File Read

Social

2026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts

No posts seen yet on X, Bluesky, Mastodon, Hacker News or GitHub.

Vendor statements

Quoted
CloudflareWAF Managed Rules1 quoteBlocks by default

Named by 2026-08-04; the first entry is an update, so the rule may be older.

2026-08-04Updated…3a5b40d6Default: BlockSource
Rails - Arbitrary File Read & RCE - CVE:CVE-2026-66066. Previous action: Block. New action: Block. This was labeled as File Upload - RCE.
AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. The rule tables name CVEs but carry no dates, so Azure is left out of every time-to-rule figure.

Google CloudCloud Armor preconfigured WAF rulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. Google names few CVEs: the release notes start in May 2024 and the rules reference lists CVEs without dates. Its cve-canary rules are opt-in.

FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)1 quoteRule published

First rule 2026-09-16, 48 days after the CVE was published.

2026-09-16New rule200009375Source
Added: signature 200009375 "Ruby on Rails "Active Storage" Arbitrary File Read" (Information Leakage, risk Medium), systems: Ruby. References: CVE-2026-66066.
AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. CRS rarely names CVEs: it relies on generic detections. Our own lab measures what it actually blocks.