# CVE-2026-126081: Action Pack: Possible Strong Parameters bypass in Parameters#each_key


- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 10 Nov 2026
- **Updated:** 10 Nov 2026
- **Also known as:** DEBIAN-CVE-2026-126081, GHSA-wm3x-v3qw-4jh3, UBUNTU-CVE-2026-126081

## What is CVE-2026-126081?

CVE-2026-126081 is a high-severity vulnerability in rails, published on 10 Nov 2026. 

### Official description

Action Pack is a framework for handling and responding to web requests. Prior to 8.1.4.1 and 8.0.5.2, 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. An application is affected if it passes the return value of ActionController::Parameters#each_key, called with a block, to mass assignment. Rails itself makes no such call. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

Weakness: CWE-915 (Improperly Controlled Modification of Dynamically-Determined Object Attributes)

## Which versions are affected by CVE-2026-126081?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `actionpack` | RubyGems | All versions | 8.0.5.2 |
| `actionpack` | RubyGems | From 8.1.0.beta1 | 8.1.4.1 |

## How do I fix CVE-2026-126081?

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

## Is CVE-2026-126081 being exploited?

There is no known exploitation of CVE-2026-126081 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126081 and fix it if it is affected.

What it is: CVE-2026-126081 is a high-severity vulnerability in rails, published on 10 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-126081 in the wild and no public exploit code.

Affected packages and fixed versions:
- actionpack (RubyGems): affected all versions; fixed in 8.0.5.2
- actionpack (RubyGems): affected from 8.1.0.beta1; fixed in 8.1.4.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-126081/ (Markdown: https://insights.sbomify.com/CVE-2026-126081/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126081
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126081
- OSV: https://osv.dev/vulnerability/CVE-2026-126081

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126081/
Summaries are generated and may contain mistakes; the official description above is the record.