Bug 2571244 (CVE-2026-126071)

Summary: CVE-2026-126071 activestorage: Active Storage: Denial of Service via thread exhaustion from streaming storage errors
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akostadi, amasferr, dmayorov, eshamard, jlledo, jvasik, kaycoth, pantinor, rblanco, tsedmik
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Active Storage component of Ruby on Rails. When files are served using proxy streaming, an error from the underlying cloud storage service partway through a download fails to properly close the streaming buffer. As a result, the server thread handling the request remains blocked until the application process restarts. A remote attacker can exploit this flaw by repeatedly triggering failed or interrupted downloads to exhaust server worker threads, leading to a Denial of Service (DoS).
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-11-10 20:58:19 UTC 
Active Storage makes it simple to upload and reference files in cloud services and attach those files to Active Record objects. From 8.0 until 8.0.5.2 and 8.1.4.1, when Active Storage serves a file through its proxy controllers, ActiveStorage::Streaming#send_blob_stream handles an error from the storage service by calling head to send a 404 or 500 response. If the error occurs after the first chunk has been written, the response is already committed, and head replaces the response body while the server is still reading the original ActionController::Live buffer. That buffer is never closed, so the server thread handling the request blocks until the process restarts. Repeated failed downloads could exhaust the server's threads, possibly resulting in a DoS vulnerability. Applications are affected when they store files on a service that streams a download in several requests, such as Amazon S3, an S3-compatible service or Google Cloud Storage, and draw Active Storage's default routes. The proxy routes are drawn whether or not proxy mode is the default for the application. A file deleted while it is being served, or any other storage error partway through a download, triggers the condition. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.