Action Pack: Possible Strong Parameters Bypass in Parameters#each_key

Exploitation

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

CVSS

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

EPSS

• CVE-2026-126081: 0.63% estimated exploitation activity in the next 30 days; percentile 50.57 (FIRST EPSS, 2026-11-14). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact `ActionController::Parameters#each_key` delegates to the internal `ActiveSupport::HashWithIndifferentAccess` that holds the request parameters, so when called with a block it returns that hash instead of the `Parameters` instance. The hash does not respond to `permitted?`, so Active Model mass assignment (`new`, `assign_attributes`, `update`) accepts it without raising `ActiveModel::ForbiddenAttributesError`. An application that passes the return value of `each_key` to mass assignment could allow a remote, unauthenticated attacker to set attributes that the application does not permit, such as an authorization flag. This is an incomplete fix of CVE-2020-8164, which made `each`, `each_pair` and `each_value` return the `Parameters` instance but left `each_key` delegated.

Details The fixed releases define `Parameters#each_key` to yield each key and return the `Parameters` instance when given a block, as `each`,…

Published by the source

12 Nov 2026, 23:37 UTC

Last modified by the source

12 Nov 2026, 23:45 UTC

Source last checked

13 Nov 2026, 06:40 UTC

1. Revision 2 · amended · 13 Nov 2026

   Amended from osv record GHSA-wm3x-v3qw-4jh3

2. Revision 1 · created · 13 Nov 2026

   Published from ghsa record GHSA-wm3x-v3qw-4jh3

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# Patch Next advisory brief: CVE-2026-126081

Advisory: Action Pack: Possible Strong Parameters Bypass in Parameters#each_key
IDs: CVE-2026-126081, GHSA-wm3x-v3qw-4jh3
Record: https://patchnext.com/advisories/cve-2026-126081 (revision 2, source checked 13 Nov 2026, 06:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: actionpack 8.1.4.1, 8.0.5.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems actionpack: 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 actionpack: 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 actionpack.
- 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-wm3x-v3qw-4jh3 (GitHub-reviewed advisory GHSA-wm3x-v3qw-4jh3 lists affected ranges: RubyGems actionpack >=8.1.0.beta1 =0 <8.0.5.2)
- Verified: https://osv.dev/vulnerability/GHSA-wm3x-v3qw-4jh3 (OSV record GHSA-wm3x-v3qw-4jh3 lists affected ranges: RubyGems actionpack >=8.1.0.beta1 =0 <8.0.5.2 (fixed))

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