Snort mailing list archives
Trouble with pass rule
From: Carl <lists () carldunham com>
Date: Mon, 28 Apr 2003 18:03:25 -0400
Am I just stupid, or what? I am getting a bunch of false positives on CID 1322: alert ip $EXTERNAL_NET any -> $HOME_NET any ( sid: 1322; rev: 4; msg: "BAD TRAFFIC bad frag bits"; fragbits: MD; classtype: misc-activity;) The systems: uname -a output (LVS kernel from ultramonkey.org): Linux penguin 2.4.18-27.8.0.um.1 #1 Thu Mar 20 14:02:22 JST 2003 i686 i686 i386 GNU/Linux Snort 2.0.0 SnortCenter v1.0 (beta) ACID v0.9.6b23 The variable settings: var HOME_NET [192.168.0.0/24,10.27.0.0/16] var EXTERNAL_NET any Example alert (from /var/log/snort/alert): [**] [1:1322:4] BAD TRAFFIC bad frag bits [**] [Classification: Misc activity] [Priority: 3] 04/28-17:50:18.327281 10.27.13.211 -> 10.27.255.255 UDP TTL:64 TOS:0x0 ID:30423 IpLen:20 DgmLen:1500 DF MF Frag Offset: 0x0172 Frag Size: 0x0014 I added the following pass rule, and set snort to run with the -o flag: var EPP_CHATTERS 10.47.0.0/16 pass ip $EPP_CHATTERS any -> $HOME_NET any ( sid: 1000001; rev: 7; fragbits: MD;) But I still get the alerts. The traffic is a local application protocol that uses large UDP datagrams that get fragmented into 1500-bytes IP packets (plus one for the leftover). All but the final leftover have the DF and MF flags set, as shown in the alert. The final has DF only, and isn't alerting. I also removed CID 521 (MISC Large UDP Packet) which this was triggering as well. As you can see (rev: 7), I tried a few things, like making it UDP vs. IP, adding the UDP ip_proto: 17, stuff like that. Any ideas? I can send more traces if that helps. Although some of the packets have sensitive data, I can try to black it out. Thanks. Carl ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ Snort-users mailing list Snort-users () lists sourceforge net Go to this URL to change user options or unsubscribe: https://lists.sourceforge.net/lists/listinfo/snort-users Snort-users list archive: http://www.geocrawler.com/redir-sf.php3?list=snort-users
Current thread:
- Trouble with pass rule Carl (Apr 28)
- <Possible follow-ups>
- Re: Trouble with pass rule Neil Dickey (Apr 29)
- Re: Trouble with pass rule Carl (Apr 29)