CVE-2026-126077 Action Pack: Possible sensitive session information leak in Active Storage proxy mode
- Exploited in the wild
- Not known
- Fix
- Available
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
Which versions are affected by CVE-2026-126077?
2 open source packages ship an affected version, including actionpack.
| Package | 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.
Sources
Also known as DEBIAN-CVE-2026-126077, GHSA-x6mj-8jx9-qhqv, UBUNTU-CVE-2026-126077.