{"attribution":"This product uses data from the NVD API but is not endorsed or certified by the NVD.","cve":{"id":"CVE-2026-126075","sourceIdentifier":"security-advisories@github.com","published":"2026-11-10T21:19:25.880","lastModified":"2026-11-10T21:19:25.880","vulnStatus":"Received","cveTags":[],"descriptions":[{"lang":"en","value":"Active Support is a collection of utility classes and standard library extensions used by Rails and other Ruby projects. From 8.1 until 8.1.4.1, ActiveSupport::MessagePack serializes an ActiveSupport::SafeBuffer as its bytes alone and deserializes it as a new SafeBuffer, so a buffer that is no longer html_safe? (for example, one mutated in place with gsub!) is restored as html_safe. If such a buffer holds untrusted input and is stored through a MessagePack serializer, rendering it after it is loaded bypasses ERB auto-escaping, possibly leading to XSS. Applications on Rails 8.1 are affected if they use a MessagePack serializer, such as config.action_dispatch.cookies_serializer = :message_pack or :message_pack_allow_marshal, or serializer: :message_pack for Rails.cache, ActiveSupport::MessageVerifier or ActiveSupport::MessageEncryptor, and store a SafeBuffer that was mutated in place with untrusted input. Rails 8.0 and earlier do not serialize SafeBuffer with MessagePack and are not affected. This issue is fixed in version 8.1.4.1."}],"affected":[{"source":"security-advisories@github.com","affectedData":[{"vendor":"rails","product":"rails","versions":[{"version":"\u003e= 8.1, \u003c 8.1.4.1","status":"affected"}]}]}],"metrics":{"cvssMetricV31":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N","baseScore":4.7,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"REQUIRED","scope":"CHANGED","confidentialityImpact":"LOW","integrityImpact":"LOW","availabilityImpact":"NONE"},"exploitabilityScore":1.6,"impactScore":2.7}]},"weaknesses":[{"source":"security-advisories@github.com","type":"Primary","description":[{"lang":"en","value":"CWE-79"}]}],"references":[{"url":"https://github.com/rails/rails/commit/4ca090665976e6fbc471c38689b399f84b43cdc7","source":"security-advisories@github.com"},{"url":"https://github.com/rails/rails/releases/tag/v8.1.4.1","source":"security-advisories@github.com"},{"url":"https://github.com/rails/rails/security/advisories/GHSA-2w9f-fxwj-w2qf","source":"security-advisories@github.com"}]}}