Undertow, a web server component, is vulnerable to HTTP request smuggling via a flaw triggered by sending '\r\r\r' as a header block terminator. This vulnerability affects certain versions of Undertow and can be exploited when used with some proxy servers like older Apache Traffic Server and Google Cloud Classic Application Load Balancer. Exploitation may lead to unauthorized access or manipulation of web requests. A patch is available in versions 2.3.25.Final and 2.2.40.Final.