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CVE-2026-126084 Active Storage: Unsigned Content-Type in Active Storage GCS direct uploads with cache_control

4.7 mediumEPSS 0.1%Fix available

Medium (4.7) in rails rails. EPSS 0.1% estimated probability of exploitation activity in the next 30 days. Fixed in activestorage 8.0.5.2, 8.1.4.1.

On this page
Active Storage makes it simple to upload and reference files in cloud services and attach those files to Active Record objects. Prior to 8.1.4.1 and 8.0.5.2, when a GCS service is configured with the cache_control option, ActiveStorage::Service::GCSService#url_for_direct_upload signs direct-upload URLs with V4, and the V4 signature covers only the Cache-Control and Host headers. A direct-upload client can therefore send a Content-Type of its choosing, and can omit the declared Content-MD5, without invalidating the URL. GCS stores the supplied content type as object metadata, which takes precedence over the response-content-type that Active Storage sets on download URLs, so an uploaded object could be served as inline HTML under the application's bucket path on storage.googleapis.com. Script in such an object runs on the storage origin rather than the application's, but could register a Service Worker scoped to the bucket path and read or replace a victim's later responses for signed URLs in that bucket. Applications that use the GCS service with cache_control configured and accept direct uploads are affected. GCS services without cache_control sign with V2 and are not affected. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

Severity

CVSS 3.1

4.7 medium
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS
0.1% estimated probability of exploitation activity in the next 30 days; 3rd percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
CISA's assessment (SSVC)
Exploitation: none · Automatable: no · Technical impact: partial, assessed 2026-11-12. From CISA's Vulnrichment in the CVE List: whether it is exploited, whether exploiting it can be automated, and how much control it gives.
CWE
CWE-345 Insufficient Verification of Data Authenticity
OWASP Top 10
A08:2025 Software or Data Integrity Failures
Published
Modified
Assigned by
GitHub_M (CNA)
NVD analysis
Awaiting analysis
Record from
the NVD, synced

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Affected

Versions

From the CNA's record in the CVE List.

ProductAffected
rails>= 8.1, < 8.1.4.1
rails< 8.0.5.2

Fix and patched versions

  • activestorage (RubyGems): fixed in 8.1.4.1, 8.0.5.2

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-3w93-6hmw-whh4RubyGemsactivestorage>=8.1.0.beta1 <8.1.4.18.1.4.1
GHSA-3w93-6hmw-whh4RubyGemsactivestorage<8.0.5.28.0.5.2

Linux distributions

DistributionReleasePackageFixed inAdvisory
Debian12, 13, 14railsno fix listedDEBIAN-CVE-2026-126084
Ubuntu24.04:LTS, 26.04:LTS, 26.10 and 4 morerailsno fix listedUBUNTU-CVE-2026-126084

From the distributions' data via OSV.dev: the Debian Security Tracker; Ubuntu Security Notices © Canonical Ltd., CC BY-SA 4.0. Modified: reformatted and linked to CVE records. Credits. On the distributions' own pages: Debian · Ubuntu.

Attack patterns (CAPEC)

The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits. More on the page of CWE-345 (12).

References

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