CVE-2026-33173: Rails Active Storage has possible content type bypass via metadata in direct uploads

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-24 · updated 2026-06-17
Weakness: CWE-925

Description

Active Storage allows users to attach cloud and local files in Rails applications. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, `DirectUploadsController` accepts arbitrary metadata from the client and persists it on the blob. Because internal flags like `identified` and `analyzed` are stored in the same metadata hash, a direct-upload client can set these flags to skip MIME detection and analysis. This allows an attacker to upload arbitrary content while claiming a safe `content_type`, bypassing any validations that rely on Active Storage's automatic content type identification. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Affected products

Ruby on Rails: before 7.2.3.1; from 8.0.0 before 8.0.4.1; from 8.1.0 before 8.1.2.1 — fixed in 7.2.3.1, 8.0.4.1, 8.1.2.1
Rubygems Activestorage: from 8.1.0.beta1 before 8.1.2.1; from 8.0.0.beta1 before 8.0.4.1; before 7.2.3.1; 8.1.0, 8.1.0.beta1, 8.1.0.rc1, 8.1.1, 8.1.2, 8.0.0 (+170) — fixed in 8.1.2.1, 8.0.4.1, 7.2.3.1

How to fix

Upgrade to a fixed version: Ruby on Rails 7.2.3.1, 8.0.4.1, 8.1.2.1; Rubygems Activestorage 8.1.2.1, 8.0.4.1, 7.2.3.1. Check the vendor advisory for mitigations.

References

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