[pdw]

HTTP is saved here because headers aren't allowed to contain control characters. A server that is strict enough to only recognize CRLF will hopefully also be strict enough to reject requests that contain invalid characters.

The situation is different with SMTP, see https://www.postfix.org/smtp-smuggling.html

[kragen]

Hopefully is not a good word to see in a argument that a software proposal is secure.

Myself, I've written an HTTP server that is strict enough to only recognize CRLF, because recognizing bare CR or LF would require more code†, but it doesn't reject requests that contain invalid characters. It wouldn't open a request-header-smuggling hole in my case because it doesn't have any proxy functionality.

One server is a small sample size, and I don't remember what the other HTTP servers I've written do in this case.

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† http://canonical.org/~kragen/sw/dev3/httpdito-readme http://canonical.org/~kragen/sw/dev3/server.s