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TUCoPS :: Security App Flaws :: win5595.htm

Raptor Firewall predicatble TCP Initial Sequence Number

5th Aug 2002 [SBWID-5595]

	Raptor Firewall predicatble TCP Initial Sequence Number


	 Raptor Firewall 6.5 (Windows NT)

	 Raptor Firewall V6.5.3 (Solaris)

	 Symantec Enterprise Firewall 6.5.2 (Windows 2000 and NT)

	 Symantec Enterprise Firewall V7.0 (Solaris)

	 Symantec Enterprise Firewall 7.0 (Windows 2000 and NT)

	 VelociRaptor Model 500/700/1000

	 VelociRaptor Model 1100/1200/1300

	 Symantec Gateway Security 5110/5200/5300 



	In   Kristof   Philipsen   []   of    Ubizen
	Luxembourg                   [] advisory :

	During the transport and forwarding of packets, Initial  Sequence  Numbers
	("ISNs") are generated by the Raptor Firewall's IP stack. A weakness  in
	the generation of these ISNs could allow  a  remote  attacker  to  easily
	predict  the  sequence  numbers  for a  certain session.

	The generation of the ISNs is based  on  two  factors:  the  source  and
	destination port, and the source and destination IP. For a single  connection,
	there is an initial sequence number which will not change for a  certain
	[long] amount of time. An example connection ("session") can be  described
	as follows:

	 session = {[src ip:src port] [dst ip:dst port]}


	An ISN is attributed to a specific sessions  for  a  certain  amount  of
	time. Below are some excerpts of real-life  tests  performed  against  a
	Raptor Firewall, demonstrating this vulnerability. The  following  tests
	sends SYN packets from a  source  address  [x.x.x.x]  on  a  source-port
	[1700] to a destination  address  [z.z.z.z]  on  a  destination  port  [80]
	over a period of several minutes.



	Timeline      Connection                      ISN             Delta 


	10:33:05      x.x.x.x:1700 -> z.z.z.z:80      2088144436      -

	10:33:06      x.x.x.x:1700 -> z.z.z.z:80      2088144436      0

	10:33:07      x.x.x.x:1700 -> z.z.z.z:80      2088144436      0


	10:35:30      x.x.x.x:1700 -> z.z.z.z:80      2088144436      0

	10:35:31      x.x.x.x:1700 -> z.z.z.z:80      2088144436      0

	10:35:32      x.x.x.x:1700 -> z.z.z.z:80      2088144436      0


	10:50:43      x.x.x.x:1700 -> z.z.z.z:80      2088144436      0

	10:50:44      x.x.x.x:1700 -> z.z.z.z:80      2088144436      0

	10:50:45      x.x.x.x:1700 -> z.z.z.z:80      2088144436      0



	As shown above, this test clearly shows that the Initial Sequence  Number
	does not change for a significant amount of time.  Another  test  showed
	that when an ISN is assigned to a session,  this  session  and  ISN  are
	stored for future use for a certain amount of  time,  regardless  whether
	or not several new sessions are established from the same source IP.

	This issue has been reproduced against 6 Raptor  Firewalls,  each  belonging
	to different administrative bodies.

	* The ISN for each session is different,   but for a single session 

	  the ISN doesn't change for a considerable amount of time.


	* This  could  possibly  allow  an attacker to  hijack the session.


	* This issue affects all vulnerabilities handled  by the  Raptor IP

	  stack, including  all  sessions  to  and  traversing  the  Raptor




	Symantec has released HotFixes to resolve this issue. They can be  found
	at the following locations:

	Technical Bulletin:


	Patches and HotFixes:


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