Active Storage: Possible DoS vulnerability in Active Storage filename handling

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.3 · CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Impact `ActiveStorage::Filename#base` and `#extension_with_delimiter`, and therefore `#extension`, pass the stored filename unmodified to `File.basename` and `File.extname`, which raise `ArgumentError` when the name contains a NUL byte. Active Storage stores the client-supplied filename verbatim, so a user who is permitted to upload an attachment could persist such a filename on databases that accept NUL bytes in string columns, such as SQLite and MySQL/MariaDB. Each subsequent request that builds a variant or preview of the blob, opens it, or renders it as an Action Text attachment then raises, possibly resulting in a persistent DoS vulnerability for the pages that display the blob until it is purged or its filename is corrected. Applications that use PostgreSQL are not affected, because PostgreSQL rejects the row.

Details `Filename#base` and `#extension_with_delimiter` now derive from `Filename#sanitized`, the form that `Filename#to_s` and the `Content-Disposition` header…

Published by the source

10 Nov 2026, 21:33 UTC

Last modified by the source

10 Nov 2026, 21:45 UTC

Source last checked

11 Nov 2026, 07:35 UTC

1. Revision 2 · amended · 11 Nov 2026

   Amended from osv record GHSA-p2pm-g2h6-7j5j

2. Revision 1 · created · 10 Nov 2026

   Published from ghsa record GHSA-p2pm-g2h6-7j5j

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# Patch Next advisory brief: CVE-2026-126074

Advisory: Active Storage: Possible DoS vulnerability in Active Storage filename handling
IDs: CVE-2026-126074, GHSA-p2pm-g2h6-7j5j
Record: https://patchnext.com/advisories/cve-2026-126074 (revision 2, source checked 11 Nov 2026, 07:35 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: activestorage 8.1.4.1, 8.0.5.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems activestorage: affected >= 8.1.0.beta1, < 8.1.4.1; < 8.0.5.2; fixed in 8.0.5.2, 8.1.4.1

## Suggested inspection (read-only)
- RubyGems activestorage: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on activestorage.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-p2pm-g2h6-7j5j (GitHub-reviewed advisory GHSA-p2pm-g2h6-7j5j lists affected ranges: RubyGems activestorage >=8.1.0.beta1 =0 <8.0.5.2)
- Verified: https://osv.dev/vulnerability/GHSA-p2pm-g2h6-7j5j (OSV record GHSA-p2pm-g2h6-7j5j lists affected ranges: RubyGems activestorage >=8.1.0.beta1 =0 <8.0.5.2 (fixed))

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