Phenoelit Advisory <wir-haben-auch-mal-was-gefunden #(0815++)++>

[ Authors ]
	FX		<fx@phenoelit.de>
	FtR 		<ftr@phenoelit.de>
	kim0 		<kim0@phenoelit.de>

	Phenoelit Group	(http://www.phenoelit.de)

[ Affected Products ]
	Cisco IOS - several versions

	Known vulnerable combinations:
		Cisco 1005	IOS 11.0(18)
		Cisco 1603	IOS 11.3(11b)
		Cisco 1603	IOS 12.0(3)
		Cisco 2503	IOS 11.0(22a)
		Cisco 2503	IOS 11.1(24a)

	Known to be not vulnerable:
		Cisco 1603	IOS 12.1(11)
		Cisco 1603	IOS 12.2(5)
		Cisco 2503	IOS 11.2(26a)
		Cisco 2503	IOS 11.3(11b)
		Cisco 2503	IOS 12.0(19)

	Cisco Bug ID: 		CSCdx32056

[ Vendor communication ]
	11/16/2001	
	    to
	05/05/2002	Contacted Cisco 8 times over past 6 months concerning 
			status.
	05/07/2002	Gaus says Cisco developers assigned a low priority to
			the bug.
	05/11/2002	Provide a copy of this file to Cisco prior to
			publication.
	05/20/2002	Final corrections by Cisco included.
	05/21/2002	Info from Cisco: Fix available shortly.

[ Overview ]
	Cisco Systems IOS is vulnerable to a denial-of-service attack using
	ICMP Redirect messages.

	When flooded with ICMP redirect messages, the IOS uses up all it's
	memory to store the new host routes. The device is then unable to
	perform operations that need additional memory such as receiving
	routing updates and accepting inbound telnet(1) connections.
	
[ Description ]
	ICMP redirect messages are used in IP networks to inform a sending
	device about inefficient routing. Cisco IOS software stores redirect
	messages it receives in memory for further consultation. They do not
	become part of the normal routing table.

	When generating ICMP redirect messages with random IP addresses in the
	"offending packet" section of the ICMP frame, IOS will include this IP
	address in it's ICMP redirection table. In the vulnerable versions of
	IOS, this table has no size limit. Later versions of IOS enforce a
	limit of 16000 redirects and therefore limit the amount of used
	memory to approximately 1.16MB.

	Some device/IOS combinations tested were unable to perform normal IP
	routing for a limited time, but most combinations continued to
	function as a router. In some cases, even access to the console was 
	denied because of low memory.

	According to Gaus (gaus@cisco.com), affected devices should recover
	after 4 hours since the redirect table entries time out. However,
	vulnerable versions tested did not recover.

[ Example ]
	To generate random ICMP redirect messages, a sender tool is available 
	at http://www.phenoelit.de/irpas/icmp_redflod.c, which has to be
	linked with the IRPAS packet library.

	linuxbox# cd /where/irpas/is
	linuxbox# make libpackets.a
	linuxbox# gcc -o icmp_redflod -I. -L. icmp_redflod.c -lpackets
	linuxbox# ./icmp_redflod -i eth0 -D <destination_ip> -G <fake_gateway>

	On high bandwidth networks, the command line switch -w0 can be used to
	increase the sending rate.

[ Solution ]

	Filter inbound ICMP redirect messages or update your IOS to either a
	not vulnerable release or a fixed version when these become available.

[ Side note ]

	Microsoft Windows 98 is also vulnerable to this attack. 
	Not tested any further.

[ end of file ]