This vulnerability may allow for request smuggling attacks, potentially resulting in an unspecified system caching incorrect content. The bug is an error in how to parse a chunked message body. The RFC tells to use only CRLF sequence to end a line: https://www.rfc-editor.org/rfc/rfc9112.html#name-chunked-transfer-coding However, Varnish has up until now mistakenly treated white-spaces as line ending as well. This allows a client to construct a HTTP/1 request to smuggle another malicious request in the body of the first request. When this is used against an endpoint that is blindly forwarding HTTP requests, it can lead to ways for this client to abuse this behavior of Varnish.