# CVE-2026-126077: Action Pack: Possible sensitive session information leak in Active Storage proxy mode


- **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/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-2026-126077, GHSA-x6mj-8jx9-qhqv, UBUNTU-CVE-2026-126077

## What is CVE-2026-126077?

CVE-2026-126077 is a medium-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, When ActionDispatch::Cookies reads a signed or encrypted cookie that was written under a rotated secret (config.action_dispatch.cookies_rotations) or in the format that a :hybrid cookie serializer migrates from, it writes the cookie back to the response in the current format, and that write ignores request.session_options[:skip]. ActiveStorage::DisableSession relies on that option to keep the session cookie off the public, immutable responses of the Active Storage proxy controllers, but those controllers still load the session, so a request carrying an old-format session cookie could receive the rewritten session cookie in Set-Cookie on a cacheable response. A shared cache that stores such a response together with its Set-Cookie header could then serve one user's session to later requesters of the same URL, or serve an attacker's session to other users. Applications are affected when they serve Active Storage files through the proxy controllers, have a cookie rotation or a :hybrid serializer migration configured, and run behind a cache that stores Set-Cookie on public responses. This is a path around the fix for CVE-2024-26144. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-126077?

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-2026-126077?

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

## Is CVE-2026-126077 being exploited?

There is no known exploitation of CVE-2026-126077 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126077 and fix it if it is affected.

What it is: CVE-2026-126077 is a medium-severity vulnerability in rails, published on 10 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-126077 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-2026-126077/ (Markdown: https://insights.sbomify.com/CVE-2026-126077/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126077
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126077
- OSV: https://osv.dev/vulnerability/CVE-2026-126077

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126077/
Summaries are generated and may contain mistakes; the official description above is the record.