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Fencer Vulns
medium 5.3

CVE-2026-33173 json

Rails Active Storage has possible content type bypass via metadata in direct uploads

published 2026-03-23 7 mo ago modified 2026-09-10 59 d ago also EUVD-2026-14626 , GHSA-qcfx-2mfw-w4cg

cvss
5.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 34%
public exploits
0
none known

Summary

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.

Patch / fix

  • rubygems activestorage 7.2.3.1, 8.0.4.1, 8.1.2.1
  • rubyonrails rails 7.2.3.1, 8.0.4.1, 8.1.2.1
  • rails Debian 12 2:6.1.7.10+dfsg-1~deb12u3
  • rails Debian 13 2:7.2.2.2+dfsg-2~deb13u2
  • rails Debian 14 2:7.2.3.1+dfsg-1

debian advisories DEBIAN-CVE-2026-33173

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-33173 updated cvss 7.6

Rails: Active Storage: Rails Active Storage: Content type bypass via arbitrary metadata in direct uploads

  • Red Hat 3scale API Management Platform 2 3scale-amp21/zync, 3scale-amp22/zync, 3scale-amp24/zync, 3scale-amp25/zync, 3scale-amp26/zync, 3scale-amp20/system, +11 more
    affected: no fix available, no fix planned “Will not fix”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.40% chance of exploitation in the next 30 days, higher than 34% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 5.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
CNA 4.0 5.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/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
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
rubygems activestorage
>=8.1.0.beta1, <8.1.2.1
>=8.0.0.beta1, <8.0.4.1
<7.2.3.1
8.1.2.1
8.0.4.1
7.2.3.1

Affected products

  • rails activestorage

Classification

Weakness
  • CWE-925 Improper Verification of Intent by Broadcast Receiver
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of rails/rails published their own advisory on GitHub. Reviewed sources take precedence over it.