CVE-2026-33173 — activestorage
Fix: rails/rails@707c0f1CVE-2026-33173 is a CWE-925 vulnerability in activestorage. A fix is available for activestorage — see the affected versions and patch details below.
Rails Active Storage has possible content type bypass via metadata in direct uploads
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-33173.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
activestorage💎activestorage💎activestorageReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | activestorage | ≥ 8.1.0.beta1&&< 8.1.2.1 | 8.1.2.1bundle update activestorage --conservative |
| 💎RubyGems | activestorage | ≥ 8.0.0.beta1&&< 8.0.4.1 | 8.0.4.1bundle update activestorage --conservative |
| 💎RubyGems | activestorage | all versions | 7.2.3.1bundle update activestorage --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for activestorage, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update activestorage to 8.1.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33173 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-33173 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-33173. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-33173 in your dependencies?
O3 Security finds CVE-2026-33173 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.