Nmap Announce mailing list archives
Re: Updated scanning techniques
From: Lance Spitzner <lance () spitzner net>
Date: Sat, 9 Sep 2000 20:54:16 -0500 (CDT)
On Sat, 9 Sep 2000, Dug Song wrote:
1. -sA -sA is not the option of choice any more for newer firewalls, such as CheckPoint FW-1 ver 4.1 SP2. As most of you know, -sA is designed to validate firewall rulebases using ACK packets. However, newer firewalls only allow SYN packets to build a session in the state table, so you can no longer initiate connecitons with an ACK packet.are you sure this is what's happening? from what i've heard, upon receipt of an ACK not associated with an existing connection, Firewall-1 passes the ACK through as a window probe (no payload) and intercepts any response from the destination itself to determine if the connection actually exists (as it might in the case of a firewall reboot).
Prior to FW-1 ver 4.1 SP2, a session could be added to the state table by almost any packet, as long as the session was allowed by the rulebase. For example, if telnet is allowed, you can create a session simply be sending a ACK packet through the firewall on port 23. The ACK packet will build the session in the state table, regardless if the other system responds with any packet or not. This creates a vulnerability for DoS attacks (see http://www.securityfocus.com/vdb/bottom.html?vid=549). For details on this functionality, see my writeup at http://www.enteract.com/~lspitz/fwtable.html. Now, starting with FW-1 ver 4.1 SP2 (and I assume any version after), this functionality has been changed. Starting with this new version, ONLY a SYN packet can build a session table, regardless if the rulebase allows the packet. So, when the '-sA' option will not work with the latest version of FW-1, as all the ACK packets will be dropped. As such, I had to revert to scanning the FW-1 rulebase with -sS option (which uses SYN packets). Just confirmed this on my system :0 sent some ACK packets with hping2, nothing made it through the firewall. lance -------------------------------------------------- For help using this (nmap-hackers) mailing list, send a blank email to nmap-hackers-help () insecure org . List run by ezmlm-idx (www.ezmlm.org).
Current thread:
- Updated scanning techniques Lance Spitzner (Sep 12)
- Re: Updated scanning techniques Lennert Buytenhek (Sep 12)
- Re: Updated scanning techniques Nelson Brito (Sep 12)
- Re: Updated scanning techniques Dug Song (Sep 12)
- RE: Updated scanning techniques Robert Purdy (Sep 12)
- Re: Updated scanning techniques Lance Spitzner (Sep 12)
- Re: Updated scanning techniques Darren Reed (Sep 12)
- Re: Updated scanning techniques Lennert Buytenhek (Sep 12)