CVE-2026-33174: Rails Active Storage has a possible DoS vulnerability when in proxy mode via Range requests
Impact When serving files through Active Storage's Blobs::ProxyController, the controller loads the entire requested byte range into memory before sending it. A request with a large or unbounded Range header (e.g. bytes=0-) could cause the server to allocate memory proportional to the file size, possibly resulting in a DoS vulnerability through memory exhaustion.
Releases The fixed releases are available at the normal locations.
Other sources
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, when serving files through Active Storage's proxy delivery mode, the proxy controller loads the entire requested byte range into memory before sending it. A request with a large or unbounded Range header (e.g. bytes=0-) could cause the server to allocate memory proportional to the file size, possibly resulting in a DoS vulnerability through memory exhaustion. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-33174?
CVE-2026-33174 is classified as a denial-of-service (DoS) vulnerability due to excessive memory consumption when handling certain Range requests.
How do I fix CVE-2026-33174?
To fix CVE-2026-33174, upgrade Active Storage to versions 7.2.3.1, 8.0.4.1, or 8.1.2.1 or later.
What versions of Active Storage are affected by CVE-2026-33174?
Active Storage versions prior to 7.2.3.1, between 8.0.0.beta1 and 8.0.4.1, as well as between 8.1.0.beta1 and 8.1.2.1 are affected by CVE-2026-33174.
What causes the vulnerability CVE-2026-33174?
CVE-2026-33174 is caused by the loading of the entire requested byte range into memory by the Blobs::ProxyController, which can lead to DoS.
Is my application safe from CVE-2026-33174 if I am using a version of Active Storage above 8.1.2.1?
Yes, if you are using Active Storage version 8.1.2.1 or later, your application is not vulnerable to CVE-2026-33174.