Active Storage has possible arbitrary file read and remote code execution in Active Storage variant processing

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

• CISA KEV Not listed.
• EPSS 0.30, the 98th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

1. 31 Oct 2026, 15:16 UTC First seen by agentprime
2. 31 Oct 2026, 15:16 UTC Confirmed by OSV

Sources

• GitHub Advisory Database: GHSA-xr9x-r78c-5hrm
• OSV: GHSA-xr9x-r78c-5hrm
• github.com/rails/rails/security/advisories/GHSA-xr9x-r78c-5hrm
• github.com/rails/rails/commit/1c01bb587206ee6eb0e1179c2cef96a6a47acb1e
• github.com/rails/rails/commit/349e7a5d5b4b715af1e416db824f3c078a7d59e5
• github.com/rails/rails/commit/d79b7f4aa17dec8ce4960fef05733c8c0c7ef49a
• github.com/rails/rails
• github.com/rails/rails/releases/tag/v7.2.3.2
• github.com/rails/rails/releases/tag/v8.0.5.1
• github.com/rails/rails/releases/tag/v8.1.3.1
• github.com/rubysec/ruby-advisory-db/blob/master/gems/activestorage/CVE-2026-66066.yml
• thehackernews.com/2026/07/critical-rails-flaw-could-let.html
• www.cve.org/CVERecord/SearchResults?query=CVE-2026-66066

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.