Nmap Announce mailing list archives
Setting nmap host_timeout too low may cause DoS on inetd (?)
From: "Alek O. Komarnitsky" <alek () ast lmco com>
Date: Wed, 15 Mar 2000 10:30:34 -0700 (MST)
Nmap Folks, I think I might have a "inadvertant" denial of service attack caused by nmap on Solaris2.6{+} and HPUX10.20 machines. I recently setup a web page using nmap to do misc. port scanning; with the main intention being to look for web servers - we're trying to clamp down a bit on 'em and get 'em semi-under-control. In order for it to run super-duper fast, I added a: $NMAP_OPTIONS = "--initial_rtt_timeout 300 --host_timeout 5000"; BTW, it sure seems like rtt_timeout is actually in HUNDREDTH's of a second rather than milliseconds - since when I use this on a host that is not up; it times out in 3 seconds ... changing 300 to 1500 causes the timeout in 15 seconds (I'm using nmap Beta13 on a Solaris2.7 box). I might be a bit agressive with the host_timeout ... all hosts are semi-local-LAN/WAN ... and I'm only hitting a hundred or so specified ports; but we're just trying to do quick-n-dirty stuff, and it's cool to see the results from 500+ machines in a flash - nmap is QUITE cool! NOTE: Just using standard "TCP" scans running as a non-root user. A few percent of the scanned machines end up with a "hanging" inetd; so inbound telnet/etc. connections are no longer accepted. Interestingly enough, one can often "clear" it by doing another scan to just the targeted host. And on a few machines, inetd flatout died - so then you are basically hosed! Sun Bug ID4260432 describes a situation somewhat similar to this ... but the problem in not repeatable in any way ... the vast majority of the time; the scan just finishes and we are all happy. So ... my guess is that on those "few" boxes, I don't quite get done in time and nmap aborts, leaving some half-open connections ... which then causes inetd to crash-n-burn. Ideally, inetd should not be so fragile! ;-) Bumping the host_timeout may be all I need to do. I emphasize my attempt here is NOT to cause a DoS, but to provide a quick-n-dirty (and safe! ;-) web based scanning tool for internal use. Does any of this make sense and/or sound familier to people? Thanx, alek P.S. Apologies if I missed an archive of the Email list - if this topic has been covered elsewhere, pls point me that direction.
Current thread:
- Setting nmap host_timeout too low may cause DoS on inetd (?) Alek O. Komarnitsky (Mar 15)
- Re: Setting nmap host_timeout too low may cause DoS on inetd (?) Thomas Reinke (Mar 16)
- <Possible follow-ups>
- RE: Setting nmap host_timeout too low may cause DoS on inetd (?) Jones, Greg (Mar 16)
- RE: Setting nmap host_timeout too low may cause DoS on inetd (?) Alek O. Komarnitsky (Mar 16)
- RE: Setting nmap host_timeout too low may cause DoS on inetd (?) Jose Nazario (Mar 17)
- Re: Setting nmap host_timeout too low may cause DoS on inetd (?) LaMont Jones (Mar 17)
- RE: Setting nmap host_timeout too low may cause DoS on inetd (?) Jose Nazario (Mar 17)