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CVE-2026-66066

Vulnerability in activestorage (CVE-2026-66066)

Summary

Vulnerability in activestorage (CVE-2026-66066). Risk of unauthorized operations or information disclosure. Exploitable via secret_key_base. Mitigation: upgrade to 8.1.3.1 or later.

Original description

The description as published by the source.

Impact

In its default configuration, a Rails application that displays image variants may allow an
unauthenticated attacker to read arbitrary files from the server, including the process environment.
That environment typically holds secret_key_base and often credentials for external systems, which
may in turn allow escalation to remote code execution or lateral movement to those systems.

Details

libvips reads and writes file formats through "loaders" and "savers" (or more generally
"operations"), many of which are backed by third-party libraries. It marks some of these operations
as "unfuzzed", meaning they are unsafe for untrusted content, and several handle formats unrelated
to web images. Active Storage did not disable the unfuzzed operations, so an attacker who can upload
a crafted file and cause a variant to be generated from it may be able to invoke one.

We are aware of a mechanism by which an attacker, by uploading a crafted file, is able to cause
disclosure of the contents of arbitrary files accessible on the filesystem of the targeted
application. One specific attack chain has been reported to us (see "Disclosure" below), but we do
not assume it is the only one that exists.

Affected applications

An application is affected if it meets all of these requirements:

  • Uses libvips for Active Storage image processing. This is config.active_storage.variant_processor = :vips,
    which load_defaults 7.0 set and no later default has changed.
  • Allows image u…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-66066 has been found in activestorage.
Attackers can target a specific entry point like secret_key_base over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade activestorage to 8.1.3.1 or later.
If unsure, ask your IT team or search "activestorage CVE-2026-66066" on the vendor's site.

CVE-2026-66066 (activestorage) — CWE-1188
Attack surface: secret_key_base / activestorage / RAILS_MASTER_KEY / VIPS_BLOCK_UNTRUSTED
Patched: 8.1.3.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-1188) exists in activestorage. Attackers reach the vulnerable code path via secret_key_base.

📍 Affected scope

Check the vendor advisory for the affected versions of activestorage. Attack surface: secret_key_base / activestorage / RAILS_MASTER_KEY / VIPS_BLOCK_UNTRUSTED.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 8.1.3.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'activestorage' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'activestorage' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で activestorage を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade activestorage to 8.1.3.1

    ステージング環境で 8.1.3.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

rubygems activestorage
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"8.1.3.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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