# CVE-2026-126071: Ruby on Rails Active Storage denial of service via stream error handling

Source: https://junglewise.ai/threats/cve-2026-126071-active-storage-makes-it-simple-to-upload-and-reference-files-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-10. Updated: 2026-11-10  
License: CC BY 4.0 with a link back

CVE-2026-126071 · Severity: medium · CVSS 5.3 · Published 2026-11-10

Rails Active Storage is a file upload and attachment system for web applications. When serving files from cloud storage services like Amazon S3 or Google Cloud Storage, a storage error during download can leave server threads blocked indefinitely, exhausting server resources and causing the application to become unresponsive. Repeated failed downloads could render the entire application unavailable.

Technologies: [Ruby on Rails Active Storage](https://junglewise.ai/threats/technologies/active-storage), [activestorage (RubyGems)](https://junglewise.ai/threats/technologies/activestorage). Vendors: [Ruby on Rails](https://junglewise.ai/threats/vendors/ruby-on-rails), [RubyGems](https://junglewise.ai/threats/vendors/rubygems).

## Quick answers

**Is CVE-2026-126071 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-126071 being exploited in the wild.

**How severe is CVE-2026-126071?** Medium severity, with a CVSS score of 5.3, published 10 November 2026.

**Which products and versions are affected?** Ruby on Rails Active Storage 8.0 before 8.0.5.2, 8.1 before 8.1.4.1; activestorage (RubyGems) >= 8.1.0.beta1, < 8.1.4.1, ECOSYSTEM:introduced=8.1.0.beta1,fixed=8.1.4.1.

**Is there a fix for CVE-2026-126071?** Yes. activestorage (RubyGems): upgrade to 8.1.4.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-126071 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-126071?** Check whether you run Ruby on Rails Active Storage or activestorage (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- activestorage (RubyGems): upgrade to 8.1.4.1 or later

  ```sh
  bundle update activestorage
  ```


## Technical details

The vulnerability exists in Active Storage's proxy controller stream handling (ActiveStorage::Streaming#send_blob_stream): when a storage service error occurs after the first chunk has been written to the client, the response is already committed. The code attempts to call head() to send a 404 or 500 response, but this leaves the original ActionController::Live buffer open and unread, causing the server thread to block indefinitely. This affects applications using streaming cloud storage services and the default proxy routes.

## Affected products

- Ruby on Rails Active Storage 8.0 before 8.0.5.2, 8.1 before 8.1.4.1

## Identifiers

- CVE-2026-126071
- GHSA-4v2w-w6g6-f8f8

## Timeline

- 2026-11-10: disclosed

## References

- [https://github.com/rails/rails/commit/3c67a693fb21870ecb1222e3da59d5c491a62009](https://github.com/rails/rails/commit/3c67a693fb21870ecb1222e3da59d5c491a62009)
- [https://github.com/rails/rails/commit/655b4442de136a3701334607f634d698bf9d5b82](https://github.com/rails/rails/commit/655b4442de136a3701334607f634d698bf9d5b82)

## Related threats

- [Active Storage: Possible local file disclosure in video previews and analysis](https://junglewise.ai/threats/cve-2026-126188-active-storage-makes-it-simple-to-upload-and-reference-files-in)
- [Ruby on Rails Active Storage arbitrary file read and RCE in media processing](https://junglewise.ai/threats/cve-2026-126186-active-storage-possible-arbitrary-file-read-and-remote-code)
- [Ruby on Rails Active Storage content length bypass in Google Cloud Storage uploads](https://junglewise.ai/threats/cve-2026-126085-active-storage-possible-circumvention-of-file-size-limits-in)
- [Ruby on Rails Active Storage GCS signature bypass](https://junglewise.ai/threats/cve-2026-126084-active-storage-makes-it-simple-to-upload-and-reference-files-in)
- [Rails Active Storage persistent DoS via NUL byte filename](https://junglewise.ai/threats/cve-2026-126074-active-storage-makes-it-simple-to-upload-and-reference-files-in)