Full Disclosure mailing list archives
SQL Slammer - lessons learned
From: John.Airey () rnib org uk
Date: Mon, 3 Feb 2003 11:23:22 -0000
I've put a lot of time into researching further into what I already know about TCP/IP connections, and this is what I've learned: The Well Known Ports are those from 0 through 1023. The Registered Ports are those from 1024 through 49151 The Dynamic and/or Private Ports are those from 49152 through 65535 (See http://www.iana.org/assignments/port-numbers) Originally, services ran on the Well Known Ports only (after all, 1024 is more than enough, since no-one would ever need more than 640KB of memory, would they?). In time these spilled onto the Registered Ports. The last range is a recent addition by ICANN/IANA. They don't appear in RFC 1700 (now obsolete) http://www.rfc-editor.org/rfc/rfc1700.txt. However, the Registered Ports have been used by TCP/IP stacks for returning connections. ie, you connect to a web site on port 80 and the connection to you comes back to one of these ports, chosen at random. (The only exception that I know to this is NTP, which uses UDP port 123 at both ends of the connection). So simply blocking a port at a router may mean that legitimate access is broken since the workstation has no way of knowing in advance that any router has blocked this port. That gives a 64511/1 chance of breaking access. For large organisations (or ISPs) with thousands of workstations, blocking a Registered Port would result in numerous failures. This is clearly unacceptable. A long term solution would be to separate port usage in IPv6, if this has not already been done. ie, to keep a range of numbers that are only ever used for connecting to external machines and the IPv6 stacks stick to this range. This will allow for better filtering by ISPs too, although someone will probably still find a way of getting worms onto this range. It is sadly too late now to fix the large number of "broken" IPv4 stacks. Clearly therefore there will always be a demand for stateful firewalls, whether on the workstation or as separate hardware. These can block connections being created to the Registered Ports that do not already exist. - John Airey, BSc (Jt Hons), CNA, RHCE Internet systems support officer, ITCSD, Royal National Institute of the Blind, Bakewell Road, Peterborough PE2 6XU, Tel.: +44 (0) 1733 375299 Fax: +44 (0) 1733 370848 John.Airey () rnib org uk Nearly everything we believe is second hand. For example, less than 500 people have seen the Earth from space, yet the majority of people believe it is round (OK pedants, an oblate sphere). - NOTICE: The information contained in this email and any attachments is confidential and may be legally privileged. If you are not the intended recipient you are hereby notified that you must not use, disclose, distribute, copy, print or rely on this email's content. If you are not the intended recipient, please notify the sender immediately and then delete the email and any attachments from your system. RNIB has made strenuous efforts to ensure that emails and any attachments generated by its staff are free from viruses. However, it cannot accept any responsibility for any viruses which are transmitted. We therefore recommend you scan all attachments. Please note that the statements and views expressed in this email and any attachments are those of the author and do not necessarily represent those of RNIB. RNIB Registered Charity Number: 226227 Website: http://www.rnib.org.uk _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html
Current thread:
- SQL Slammer - lessons learned John . Airey (Feb 03)
- Re: SQL Slammer - lessons learned Henrik Lund Kramshøj (Feb 03)
- Re: SQL Slammer - lessons learned David Howe (Feb 03)
- <Possible follow-ups>
- Re: SQL Slammer - lessons learned David Howe (Feb 03)
- AOL refuses to help AIM users ATD (Feb 03)
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- Re: AOL refuses to help AIM users ATD (Feb 03)
- Re: AOL refuses to help AIM users Rick Updegrove (Feb 03)
- Re: AOL refuses to help AIM users ATD (Feb 03)
- AOL refuses to help AIM users ATD (Feb 03)
- Re: AOL refuses to help AIM users Berend-Jan Wever (Feb 04)
- RE: SQL Slammer - lessons learned Paul Schmehl (Feb 05)