CVE-2026-126081: Action Pack: Possible Strong Parameters bypass in Parameters#each_key

Action Pack is a framework for handling and responding to web requests. Prior to 8.1.4.1 and 8.0.5.2, ActionController::Parameters#eachkey delegates to the internal ActiveSupport::HashWithIndifferentAccess that holds the request parameters, so when called with a block it returns that hash instead of the Parameters instance. The hash does not respond to permitted?, so Active Model mass assignment (new, assignattributes, update) accepts it without raising ActiveModel::ForbiddenAttributesError. An application that passes the return value of eachkey to mass assignment could allow a remote, unauthenticated attacker to set attributes that the application does not permit, such as an authorization flag. This is an incomplete fix of CVE-2020-8164, which made each, eachpair and eachvalue return the Parameters instance but left eachkey delegated. An application is affected if it passes the return value of ActionController::Parameters#eachkey, called with a block, to mass assignment. Rails itself makes no such call. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.