How severe is CVE-2026-126067?

CVE-2026-126067 has a CVSS score of 3.1/10, rated LOW. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-126067?

CVE-2026-126067 affects the following packages: actionpack (RubyGems), actionpack (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2026-126067?

Update actionpack to 8.1.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-126067 is resolved across your whole dependency graph.

How do I detect CVE-2026-126067 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for actionpack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-126067 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-126067 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-126067 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-126067?

CVE-2026-126067 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 6th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-126067?

CVE-2026-126067 is classified as Cross-Site Request Forgery (CSRF) (CWE-352). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-126067 published, and has it been updated?

CVE-2026-126067 was published on November 10, 2026 and was last updated on November 11, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎

💎 RubyGems

Not in CISA KEV

LOW severity

CVE-2026-126067 — actionpack

LOWFix: rails/rails@2d9f502

CVE-2026-126067 is a low-severity (CVSS 3.1) Cross-Site Request Forgery (CSRF) vulnerability in actionpack. A fix is available for actionpack — see the affected versions and patch details below.

Action Pack: Missing SameSite attribute on session cookies from Action Pack session stores

Also known asGHSA-gmj8-hvj3-49mw

Published

Nov 10, 2026

Updated

Nov 11, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs6th percentile — riskier than 6% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

💎actionpack💎actionpack

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Action Pack session stores other than ActionDispatch::Session::CookieStore (CacheStore, MemCacheStore, and third-party stores built on AbstractStore, AbstractSecureStore or the session mixins) write the session cookie without a SameSite attribute, regardless of config.action_dispatch.cookies_same_site_protection, which defaults to :lax. Only CookieStore applies the configured policy. In browsers that do not treat a cookie without the attribute as SameSite=Lax, a cross-site request could carry the session cookie, possibly leading to cross-site request forgery against actions that do not verify an authenticity token, such as those of API-only applications.

Applications are affected when they use a session store other than CookieStore and do not pass same_site: to config.session_store.

Details

In the fixed releases, every session store sets the session cookie's SameSite attribute from cookies_same_site_protection when its options have no :same_site key. An explicit same_site: option, including same_site: nil, and a :same_site value in a store's DEFAULT_OPTIONS still take precedence.

Workarounds

Pass same_site: when configuring the session store, for example config.session_store :cache_store, same_site: :lax.

Releases

The fixed releases are available at the normal locations.

Patches for those who cannot upgrade at once:

Credit

This issue was responsibly reported by HackerOne researcher tjvc.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`actionpack`	≥ 8.1.0.beta1&&< 8.1.4.1	8.1.4.1`bundle update actionpack --conservative`
💎RubyGems	`actionpack`	all versions	8.0.5.2`bundle update actionpack --conservative`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for actionpack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update actionpack to 8.1.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-126067 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatLow

Red Hat rates the impact of this vulnerability as Low because successful exploitation requires multiple non-standard application preconditions and user interaction on non-default browser configurations. The issue only affects deployments utilizing alternative, non-cookie session stores that have not explicitly defined…

Workaround published by Red Hat

Explicitly configure the `same_site` attribute when declaring the session store in the Rails application configuration (such as in `config/application.rb` or an environment file in `config/environments/`): ```ruby config.session_store :cache_store, same_site: :lax ``` Substitute `:cache_store` with the specific session store utilized by the application, such as `:mem_cache_store`. Caveats: Enforcing `:lax` or `:strict` SameSite policies may alter cookie transmission during third-party redirects or external identity federation flows. Ensure integrations with external authentication providers function as expected. Warning: Modifying application configuration requires restarting or reloading…

Source: Red Hat security advisory for CVE-2026-126067 (CC BY 4.0)

Frequently Asked Questions

### Impact Action Pack session stores other than `ActionDispatch::Session::CookieStore` (`CacheStore`, `MemCacheStore`, and third-party stores built on `AbstractStore`, `AbstractSecureStore` or the session mixins) write the session cookie without a `SameSite` attribute, regardless of `config.action_dispatch.cookies_same_site_protection`, which defaults to `:lax`. Only `CookieStore` applies the configured policy. In browsers that do not treat a cookie without the attribute as `SameSite=Lax`, a cross-site request could carry the session cookie, possibly leading to cross-site request forgery agai