CVE-2026-126071 Active Storage: Possible DoS vulnerability in Active Storage proxy mode via storage errors during streaming

What is CVE-2026-126071?

CVE-2026-126071 is a medium-severity vulnerability in rails, published on 10 Nov 2026.

Official description

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.

Weakness: CWE-772

Which versions are affected by CVE-2026-126071?

2 open source packages ship an affected version, including activestorage.

How do I fix CVE-2026-126071?

Upgrade activestorage to a fixed version for your release line: 8.0.5.2 or 8.1.4.1.

Is CVE-2026-126071 being exploited?

There is no known exploitation of CVE-2026-126071 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-4v2w-w6g6-f8f8, UBUNTU-CVE-2026-126071.