`Date: Thu, 3 Jun 1999 06:22:50 +0200 From: cami To: nmap-hackers@insecure.org Subject: (local?) linux DoS using nmap Good day.. I appologize if this is old but seems still to be working/active on my own server. (slackware 4.0.0). I would be interested to know which other distro's this works against. Tested against: slackware 4.0.0 debian 2.1 Redhat 6.0 I became aware of this when local users begun to launch DoS attacks. kernel:~$ nmap 127.[0-255].[0-255].[0-255] -p 21 -sT Starting nmap V. 2.12 by Fyodor (fyodor@dhp.com, www.insecure.org/nmap/) Interesting ports on localhost (127.0.0.1): Port State Protocol Service 21 open tcp ftp Interesting ports on (127.0.0.2): Port State Protocol Service 21 open tcp ftp and it keeps going untill the +/-280th packet.. Interesting ports on (127.0.1.32): Port State Protocol Service 21 open tcp ftp No ports open for host (127.0.1.33) No ports open for host (127.0.1.34) No ports open for host (127.0.1.35) etc.. etc.. I havent tested it on remote machines, but this looks like a tcp/syn flood? Anyhow, local users can shutdown any local daemon running on any port. (apache was the only service that remaining running.) The rest of the other services became unusable/(dead?). Any ideas how one could prevent this? Sorry again if this is old. Regards hotmetal of (src) hotmetal@hack.co.za ( www.hack.co.za ) (e x p l o i t m a t r i x) (world domination in progress) ----------------------------------------------------------------------------- Date: Thu, 3 Jun 1999 01:08:27 -0500 (CDT) From: Mr. Man To: cami Cc: nmap-hackers@insecure.org Subject: Re: (local?) linux DoS using nmap What kernel version are you running, and do you have SYN Cookies enabled in that kernel? Also, were all the other services that died being called >from the inetd superserver? Inetd may have died, which I think might have been a previous problem with nmap and some versions of inetd. I'm not sure which inetd is shipping with those distributions these days, but it'd be best to use an inetd that limits the amount of commections for each type of service per IP address. The inetd that ships with my slackware 3.4 box has this option: -q queuelength Sets the size of the socket listen queue to the specified value. Default is 128. Adjusting the queue size one way or the other may help stop the problem. FreeBSD's inetd has the following options which I'm not sure these distributions have. They are: -c maximum Specify the default maximum number of services that can be in-voked. May be overridden on a per-service basis with the "max-child" parameter. -C rate Specify the default maximum number of times a service can be in-voked from a single IP address in one minute; the default is un-limited. May be overridden on a per-service basis with the "max-connections-per-ip-per-minute" parameter. -R rate Specify the maximum number of times a service can be invoked in one minute; the default is 256. I hope that sheds some light on the problem. I'm pretty sure inetd has just died, which causes all services normally called form it (ftpd, telnetd, etc.) to fail. Mr. Man - Darkside Labs If at first you don't succeed, destroy all evidence that you tried. ----------------------------------------------------------------------------- Date: Thu, 3 Jun 1999 08:48:59 -0400 (EDT) From: Vidyut Luther To: Mr. Man Cc: cami , nmap-hackers@insecure.org Subject: Re: (local?) linux DoS using nmap I tested this on my slackware box and I was able to kill off port 21. As for your comment about maybe inetd dieing ? I thought that was the caseas well at first, then I tried port 22 (ssh). whats interesting to note is that my load rocketed up to around 120. cpu usage was only 20% though (results from what procmeter is displaying right now). woops load just went up to 150 and is stayin there. anyway. if i try to ssh into my linux box right now. it's not gonna happen. until i hit ctrl -c... but as a result of this. sendmail has stopped working (load over 25, I never changed that value.. don't know how many people do :/). so now we have not only disabled ssh, but also mail. Ok i'm writing this mail as i'm running nmap in another window.. and whats funny is that once it got to scanning 127.0.5.* the load went right down to 10. and ssh was running again. I did a ctrl-c and restarted nmap, and now the load is back up at around 150.. heh actually it's been at 182 for the past 4 minutes or so. yay. wierd now the same thing f the load plummeting happens.. but now it was at the 127.0.33.* mark. :/ i'm not really sure why this happens. but.. doin this temporaririly disables ssh and mail. (once the load goes down, mail starts up again, and ssh just takes forever to work, it's not really turned off. Some people might have timeouts shorter than the amount of time it takes to establish a connection. In case you're wondering the system I tested this on is a pII 233 with 128MB ram. and 128 MB swap. results of uname -a : uname -a Linux avalon 2.2.6 #3 Thu May 27 20:50:16 EDT 1999 i686 unknown (i enabled syncookies when i compiled). and I guess as the topic suggests that command itself results in a completeyly different output on freebsd. :/ Vidyut Luther "Fear leads to anger, Anger leads to Hate, Hate leads to suffering" ---Yoda(Star Wars: The Phantom Menace) http://www.linuxpowered.com http://everything.linuxpowered.com <-- Alpha(so pardon the appearance) ----------------------------------------------------------------------------- Date: Thu, 3 Jun 1999 17:16:48 +0200 From: cami To: nmap-hackers@insecure.org Subject: Re: (local?) linux DoS using nmap > What kernel version are you running, and do you have SYN Cookies enabled 2.2.5 >only ftp is affected; Sadly i'd have to say you are incorrect. To spice up the attack.. try something like this.. kernel:~$ nmap 127.0.[0-255].[0-255] -sT And what do u get? all services go bye-bye. >I assume it will recover after some time. Unfortuately, wrong again. I sat waiting for my services to come around with no luck. >so now we have not only disabled ssh. >it got to scanning 127.0.5.* the load >went right down to 10. and ssh was >running again. Very true, sshd seems to struggle but does indeed come back up (although with much difficulty.) I've managed to code a little tool that "locks" up sshd remotely rendering it useless. (along with basically any other daemon running on a linux machine) btw.. just out of interests sake, i'm running Slackware 4.0.0 with syn cookies enabled on a pII 350 and 128m ram. Please also take note i've tested this against every version of linux i can get my hands on and it _does_ work on all distributions. Anyone run this against any FreeBSD machines etc..? Regards hotmetal of (src) hotmetal@hack.co.za ( www.hack.co.za ) (e x p l o i t m a t r i x) (world domination in progress) ----------------------------------------------------------------------------- Date: Sat, 5 Jun 1999 06:24:14 -0400 (EDT) From: Ken Williams To: cami Cc: nmap-hackers@insecure.org Subject: Re: (local?) linux DoS using nmap On Thu, 3 Jun 1999, cami wrote: > Date: Thu, 3 Jun 1999 17:16:48 +0200 > From: cami > To: nmap-hackers@insecure.org > Subject: Re: (local?) linux DoS using nmap -----snip----- > Anyone run this against any FreeBSD machines > etc..? no effect at all on services or load for the following: FreeBSD 2.2.8-STABLE FreeBSD 3.1-RELEASE FreeBSD 3.2-STABLE FreeBSD 4.0-CURRENT SunOS 5.5.1 sun4u sparc SunOS 5.6 sun4u sparc SunOS 5.7 sun4u sparc SunOS 5.7 x86 -- ken ----------------------------------------------------------------------------- Date: Sun, 6 Jun 1999 11:59:32 -0300 (ADT) From: moses@pentagram.nslug.ns.ca To: nmap-hackers@insecure.org Subject: Re: (local?) linux DoS using nmap On Thu, 3 Jun 1999, cami wrote: > kernel:~$ nmap 127.0.[0-255].[0-255] -sT > > And what do u get? all services go bye-bye. If you look through your logs you'll see entries like this: Jun 6 11:54:30 pentagram inetd[327]: ftp/tcp server failing (looping), service terminated man inetd says you can change this by appending a number after the wait/nowait entry in inetd.conf: The optional ``max'' suffix (separated from ``wait'' or ``nowait'' by a dot) specifies the maximum number of server instances that may be spawned from inetd within an interval of 60 seconds. When omitted, ``max'' defaults to 40. Just kill -1 inetd to reenable. I think ssh getting slow was just ssh getting slow (from all the daemons being forked). `

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