# CVE-2026-126074: Rails Active Storage persistent DoS via NUL byte filename

Source: https://junglewise.ai/threats/cve-2026-126074-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-2026-126074 · Severity: medium · CVSS 4.3 · Published 2026-11-10

Rails Active Storage is a library that lets web applications store and manage file attachments. A flaw allows an attacker with upload permissions to craft filenames containing NUL bytes that crash the application when the files are accessed, viewed, or processed as previews—causing a persistent denial of service that persists until the malicious file is deleted. SQLite and MySQL/MariaDB databases are vulnerable; PostgreSQL automatically rejects such files.

Technologies: [activestorage (RubyGems)](https://junglewise.ai/threats/technologies/activestorage). Vendors: [Rails](https://junglewise.ai/threats/vendors/rails), [RubyGems](https://junglewise.ai/threats/vendors/rubygems).

## Quick answers

**Is CVE-2026-126074 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-126074 being exploited in the wild.

**How severe is CVE-2026-126074?** Medium severity, with a CVSS score of 4.3, published 10 November 2026.

**Which products and versions are affected?** Rails Active Storage Prior to 8.1.4.1 and 8.0.5.2; 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-2026-126074?** 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-2026-126074 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-126074?** Check whether you run 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

Active Storage passes user-supplied filenames unmodified to File.basename and File.extname, which raise ArgumentError when encountering NUL bytes. An authenticated attacker can upload a file with an embedded NUL byte to vulnerable databases (SQLite, MySQL/MariaDB), and each subsequent attempt to open, render, or create variants of the blob triggers an exception, resulting in persistent DoS. The fix sanitizes filename parts before processing to eliminate null bytes and invalid byte sequences.

## Affected products

- Rails Active Storage Prior to 8.1.4.1 and 8.0.5.2

## Identifiers

- CVE-2026-126074
- GHSA-p2pm-g2h6-7j5j

## Timeline

- 2026-11-10: disclosed

## References

- [https://github.com/rails/rails/commit/60f22af88b71eae251f112d8c0237a08a8832692](https://github.com/rails/rails/commit/60f22af88b71eae251f112d8c0237a08a8832692)
- [https://github.com/rails/rails/commit/9b0d4bef2211a2c08cab2e0ea17fa1d0efd5d47a](https://github.com/rails/rails/commit/9b0d4bef2211a2c08cab2e0ea17fa1d0efd5d47a)

## 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)
- [Ruby on Rails Active Storage denial of service via stream error handling](https://junglewise.ai/threats/cve-2026-126071-active-storage-makes-it-simple-to-upload-and-reference-files-in)