http4k (Maven artifact org.http4k:http4k-core) before 6.48.0.0, 5.42.0.0, and 4.51.0.0 ships a BasicCookieStorage (client-side cookie store used by ClientFilters.Cookies) that does not enforce RFC 6265 scoping rules for the cookie domain, path, and Secure attributes. When a single BasicCookieStorage instance is used to talk to more than one origin or scheme, cookies stored for one origin can be sent to other origins, and cookies marked Secure can be sent over plain HTTP, potentially disclosing session cookies or other sensitive values to unauthorized hosts or network observers. Clients that use a storage instance for a single origin are not affected.