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CVE-2026-126073 Action Pack: Possible cache poisoning in Action Pack content negotiation

4.8 mediumEPSS 0.4%Fix available

Medium (4.8) in rails rails. EPSS 0.4% estimated probability of exploitation activity in the next 30 days. Fixed in actionpack 8.0.5.2, 8.1.4.1.

On this page
Action Pack is a framework for handling and responding to web requests. Prior to 8.1.4.1 and 8.0.5.2, Action Pack negotiates the format of a rendered response from the Accept, X-Requested-With and, for XHR requests without Accept, Content-Type request headers, but ActionController::Rendering#_set_vary_header adds Vary: Accept only when the request carries a usable Accept header and the response has no Vary header yet. A response to a request without Accept, or to an XHR request, therefore omits the headers that selected its representation, and a response whose Vary the application set before rendering (for example Vary: Accept-Language) never gains Accept. A shared cache that honours Vary could store such a response and serve it to later clients that request a different representation, possibly leading to cache poisoning in which visitors receive, until the entry expires, a page without its layout or HTML in place of JSON. The attacker cannot choose the content of the response. Applications that render negotiated responses from actions marked public (for example with expires_in ..., public: true) behind a shared cache that honours Vary, such as Thruster or Rack::Cache, are affected. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

Severity

CVSS 3.1

4.8 medium
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L
EPSS
0.4% estimated probability of exploitation activity in the next 30 days; 37th percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
CISA's assessment (SSVC)
Exploitation: none · Automatable: no · Technical impact: partial, assessed 2026-11-12. From CISA's Vulnrichment in the CVE List: whether it is exploited, whether exploiting it can be automated, and how much control it gives.
CWE
CWE-436 Interpretation Conflict
OWASP Top 10
A06:2025 Insecure Design
Published
Modified
Assigned by
GitHub_M (CNA)
NVD analysis
Awaiting analysis
Record from
the NVD, synced

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Affected

Versions

From the CNA's record in the CVE List.

ProductAffected
rails>= 8.1, < 8.1.4.1
rails< 8.0.5.2

Fix and patched versions

  • actionpack (RubyGems): fixed in 8.1.4.1, 8.0.5.2

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-r9jg-fmfx-2gv6RubyGemsactionpack>=8.1 <8.1.4.18.1.4.1
GHSA-r9jg-fmfx-2gv6RubyGemsactionpack<8.0.5.28.0.5.2

Linux distributions

DistributionReleasePackageFixed inAdvisory
Debian12, 13, 14railsno fix listedDEBIAN-CVE-2026-126073
Ubuntu24.04:LTS, 26.04:LTS, 26.10 and 4 morerailsno fix listedUBUNTU-CVE-2026-126073

From the distributions' data via OSV.dev: the Debian Security Tracker; Ubuntu Security Notices © Canonical Ltd., CC BY-SA 4.0. Modified: reformatted and linked to CVE records. Credits. On the distributions' own pages: Debian · Ubuntu.

Attack patterns (CAPEC)

  • CAPEC-34 HTTP Response Splitting Likelihood: Medium · Severity: High
  • CAPEC-105 HTTP Request Splitting Likelihood: Medium · Severity: High
  • CAPEC-273 HTTP Response Smuggling Likelihood: Medium · Severity: High

The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits.

References

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