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From: thalm at netcabo.pt (thalm)
Subject: Strange netcat behavior

Since netcat is a widely used network tool, this may have been discussed already, but since I wasn't able to found such discussion, here goes:
 
When using netcat (Windows and Linux versions) to connect to a web server, and everytime ENTER is pressed in the command line, netcat only sends LF (0x0A) instead of CRLF (0x0D 0x0A).
ex: GET / HTTP/1.0[LF][LF]
 
when using telnet, the behavior is different:
ex: GET / HTTP/1.0[CRLF][CRLF]
 
Although webservers (IIS and probably Apache) don't mind such behavior and accept it (LF) as if it was CRLF, RFC 2616 clearly states that the HTTP Request/Response Line and HTTP Headers *MUST* be separated by a CRLF and not only by a LF.
 
Why is there such a difference between netcat and telnet behavior?
 
NOTE: I'm wondering if sometimes a webserver exploit works when HTTP "lines" are separated by [CRLF] and does not work when HTTP "lines" are separated only by [LF].
This is actually the point I am refering to...
 
Tiago Halm
http://www.kodeit.org


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