{"id":"GHSA-r9jg-fmfx-2gv6","summary":"Action Pack: Possible cache poisoning in Action Pack content negotiation","details":"### Impact\nAction 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.\n\nApplications 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.\n\n### Details\nIn the fixed releases, a rendered response whose format is not given by the URL lists `Accept` and `X-Requested-With` in `Vary`, and also `Content-Type` for an XHR request without `Accept`; when `config.action_dispatch.ignore_accept_header` is enabled, it lists only `X-Requested-With`. These fields are appended to an existing `Vary` value rather than skipped, and `Vary: *` is left unchanged. Shared caches can store more variants of such responses than before. See the Action Pack CHANGELOG for details.\n\n### Workarounds\nSet `Vary: Accept, X-Requested-With` on negotiated responses in the application, for example in an `after_action`, or do not mark negotiated responses `public`.\n\n### Releases\nThe fixed releases are available at the normal locations.\n\nPatches for those who cannot upgrade at once:\n- 8.1: https://github.com/rails/rails/commit/7a955ca36779938267c93902c47d1f55bab99b4b.patch\n- 8.0: https://github.com/rails/rails/commit/b58c107abe9c1f10c1d6a4941402c60e4dc4742c.patch\n\n### Credit\nThis issue was found by the Anthropic OSS Scanner (ANT-2026-7GHGLQGO, ANT-2026-5MT6C2R3).","aliases":["CVE-2026-126073"],"modified":"2026-11-10T21:45:03.954760453Z","published":"2026-11-10T21:26:12Z","database_specific":{"github_reviewed":true,"github_reviewed_at":"2026-11-10T21:26:12Z","nvd_published_at":null,"cwe_ids":["CWE-436"],"severity":"MODERATE"},"references":[{"type":"WEB","url":"https://github.com/rails/rails/security/advisories/GHSA-r9jg-fmfx-2gv6"},{"type":"WEB","url":"https://github.com/rails/rails/commit/7a955ca36779938267c93902c47d1f55bab99b4b"},{"type":"WEB","url":"https://github.com/rails/rails/commit/b58c107abe9c1f10c1d6a4941402c60e4dc4742c"},{"type":"PACKAGE","url":"https://github.com/rails/rails"},{"type":"WEB","url":"https://github.com/rails/rails/releases/tag/v8.0.5.2"},{"type":"WEB","url":"https://github.com/rails/rails/releases/tag/v8.1.4.1"},{"type":"WEB","url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/actionpack/GHSA-r9jg-fmfx-2gv6.yml"}],"affected":[{"package":{"name":"actionpack","ecosystem":"RubyGems","purl":"pkg:gem/actionpack"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"8.1"},{"fixed":"8.1.4.1"}]}],"versions":["8.1.0","8.1.1","8.1.2","8.1.2.1","8.1.3","8.1.3.1","8.1.4"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/11/GHSA-r9jg-fmfx-2gv6/GHSA-r9jg-fmfx-2gv6.json"}},{"package":{"name":"actionpack","ecosystem":"RubyGems","purl":"pkg:gem/actionpack"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"8.0.5.2"}]}],"versions":["0.9.0","0.9.5","1.0.0","1.0.1","1.1.0","1.10.1","1.10.2","1.11.0","1.11.1","1.11.2","1.12.0","1.12.1","1.12.2","1.12.3","1.12.4","1.12.5","1.13.0","1.13.1","1.13.2","1.13.3","1.13.4","1.13.5","1.13.6","1.2.0","1.3.0","1.3.1","1.4.0","1.5.0","1.5.1","1.6.0","1.7.0","1.8.0","1.8.1","1.9.0","1.9.1","2.0.0","2.0.1","2.0.2","2.0.4","2.0.5","2.1.0","2.1.1","2.1.2","2.2.2","2.2.3","2.3.10","2.3.11","2.3.12","2.3.14","2.3.15","2.3.16","2.3.17","2.3.18","2.3.2","2.3.3","2.3.4","2.3.5","2.3.6","2.3.7","2.3.8","2.3.8.pre1","2.3.9","2.3.9.pre","3.0.0","3.0.0.beta","3.0.0.beta2","3.0.0.beta3","3.0.0.beta4","3.0.0.rc","3.0.0.rc2","3.0.1","3.0.10","3.0.10.rc1","3.0.11","3.0.12","3.0.12.rc1","3.0.13","3.0.13.rc1","3.0.14","3.0.15","3.0.16","3.0.17","3.0.18","3.0.19","3.0.2","3.0.20","3.0.3","3.0.4","3.0.4.rc1","3.0.5","3.0.5.rc1","3.0.6","3.0.6.rc1","3.0.6.rc2","3.0.7","3.0.7.rc1","3.0.7.rc2","3.0.8","3.0.8.rc1","3.0.8.rc2","3.0.8.rc4","3.0.9","3.0.9.rc1","3.0.9.rc3","3.0.9.rc4","3.0.9.rc5","3.1.0","3.1.0.beta1","3.1.0.rc1","3.1.0.rc2","3.1.0.rc3","3.1.0.rc4","3.1.0.rc5","3.1.0.rc6","3.1.0.rc8","3.1.1","3.1.1.rc1","3.1.1.rc2","3.1.1.rc3","3.1.10","3.1.11","3.1.12","3.1.2","3.1.2.rc1","3.1.2.rc2","3.1.3","3.1.4","3.1.4.rc1","3.1.5","3.1.5.rc1","3.1.6","3.1.7","3.1.8","3.1.9","3.2.0","3.2.0.rc1","3.2.0.rc2","3.2.1","3.2.10","3.2.11","3.2.12","3.2.13","3.2.13.rc1","3.2.13.rc2","3.2.14","3.2.14.rc1","3.2.14.rc2","3.2.15","3.2.15.rc1","3.2.15.rc2","3.2.15.rc3","3.2.16","3.2.17","3.2.18","3.2.19","3.2.2","3.2.2.rc1","3.2.20","3.2.21","3.2.22","3.2.22.1","3.2.22.2","3.2.22.3","3.2.22.4","3.2.22.5","3.2.3","3.2.3.rc1","3.2.3.rc2","3.2.4","3.2.4.rc1","3.2.5","3.2.6","3.2.7","3.2.7.rc1","3.2.8","3.2.8.rc1","3.2.8.rc2","3.2.9","3.2.9.rc1","3.2.9.rc2","3.2.9.rc3","4.0.0","4.0.0.beta1","4.0.0.rc1","4.0.0.rc2","4.0.1","4.0.1.rc1","4.0.1.rc2","4.0.1.rc3","4.0.1.rc4","4.0.10","4.0.10.rc1","4.0.10.rc2","4.0.11","4.0.11.1","4.0.12","4.0.13","4.0.13.rc1","4.0.2","4.0.3","4.0.4","4.0.4.rc1","4.0.5","4.0.6","4.0.6.rc1","4.0.6.rc2","4.0.6.rc3","4.0.7","4.0.8","4.0.9","4.1.0","4.1.0.beta1","4.1.0.beta2","4.1.0.rc1","4.1.0.rc2","4.1.1","4.1.10","4.1.10.rc1","4.1.10.rc2","4.1.10.rc3","4.1.10.rc4","4.1.11","4.1.12","4.1.12.rc1","4.1.13","4.1.13.rc1","4.1.14","4.1.14.1","4.1.14.2","4.1.14.rc1","4.1.14.rc2","4.1.15","4.1.15.rc1","4.1.16","4.1.16.rc1","4.1.2","4.1.2.rc1","4.1.2.rc2","4.1.2.rc3","4.1.3","4.1.4","4.1.5","4.1.6","4.1.6.rc1","4.1.6.rc2","4.1.7","4.1.7.1","4.1.8","4.1.9","4.1.9.rc1","4.2.0","4.2.0.beta1","4.2.0.beta2","4.2.0.beta3","4.2.0.beta4","4.2.0.rc1","4.2.0.rc2","4.2.0.rc3","4.2.1","4.2.1.rc1","4.2.1.rc2","4.2.1.rc3","4.2.1.rc4","4.2.10","4.2.10.rc1","4.2.11","4.2.11.1","4.2.11.2","4.2.11.3","4.2.2","4.2.3","4.2.3.rc1","4.2.4","4.2.4.rc1","4.2.5","4.2.5.1","4.2.5.2","4.2.5.rc1","4.2.5.rc2","4.2.6","4.2.6.rc1","4.2.7","4.2.7.1","4.2.7.rc1","4.2.8","4.2.8.rc1","4.2.9","4.2.9.rc1","4.2.9.rc2","5.0.0","5.0.0.1","5.0.0.beta1","5.0.0.beta1.1","5.0.0.beta2","5.0.0.beta3","5.0.0.beta4","5.0.0.racecar1","5.0.0.rc1","5.0.0.rc2","5.0.1","5.0.1.rc1","5.0.1.rc2","5.0.2","5.0.2.rc1","5.0.3","5.0.4","5.0.4.rc1","5.0.5","5.0.5.rc1","5.0.5.rc2","5.0.6","5.0.6.rc1","5.0.7","5.0.7.1","5.0.7.2","5.1.0","5.1.0.beta1","5.1.0.rc1","5.1.0.rc2","5.1.1","5.1.2","5.1.2.rc1","5.1.3","5.1.3.rc1","5.1.3.rc2","5.1.3.rc3","5.1.4","5.1.4.rc1","5.1.5","5.1.5.rc1","5.1.6","5.1.6.1","5.1.6.2","5.1.7","5.1.7.rc1","5.2.0","5.2.0.beta1","5.2.0.beta2","5.2.0.rc1","5.2.0.rc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