[Snort-users] preprocessor sfportscan does not generate alerts

Marc Belanger mab_snort at ...125...
Fri Feb 15 17:04:54 EST 2013



Hi,
How do I troubleshoot a Snort install that generates no alert when the sfportscan preprocessor is activated?
. I have isolated the snort IDS server and a laptop on a test network. My sniffer card is eth1 with an assigned IP (dest_ip). Attacker lauches:   nmap -sS <dest_ip>   or   nmap -sT <dest_ip>. snort in sniffer mode sees packets. snort in IDS mode does not generate alerts and the libpcap (?) logfile does not grow. /etc/snort/snort.conf file was taken directly from the snort-2.9.4.tar.gz file and slightly modified (see below). I have no errors when doing snort -T , except for flowbits key 'xxxxx' errors. 
Setup :
(...)
ipvar HOME_NET anyipvar EXTERNAL_NET any
(...)
preprocessor stream5_global: track_tcp yes, \   track_udp yes, \   track_icmp no, \   max_tcp 262144, \   max_udp 131072, \   max_active_responses 2, \   min_response_seconds 5
preprocessor stream5_tcp: policy windows, detect_anomalies, require_3whs 180, \   overlap_limit 10, small_segments 3 bytes 150, timeout 180, \    ports client 21 22 23 25 42 53 79 109 110 111 113 119 135 136 137 139 143 \        161 445 513 514 587 593 691 1433 1521 2100 3306 6070 6665 6666 6667 6668 6669 \        7000 8181 32770 32771 32772 32773 32774 32775 32776 32777 32778 32779, \    ports both 80 81 311 443 465 563 591 593 636 901 989 992 993 994 995 1220 1414 1830 2301 2381 2809 3128 3702 4343 5250 7907 7001 7145 7510 7802 7777 7779 \        7801 7900 7901 7902 7903 7904 7905 7906 7908 7909 7910 7911 7912 7913 7914 7915 7916 \ 7917 7918 7919 7920 8000 8008 8014 8028 8080 8088 8118 8123 8180 8243 8280 8800 8888 8899 9080 9090 9091 9443 9999 11371 55555
preprocessor stream5_udp: timeout 180
(...)# Portscan detection.  For more information, see README.sfportscanpreprocessor sfportscan: proto  { all } scan_type { all } memcap { 10000000 } sense_level { high } logfile { /var/log/snort/portscan.log }
(...)

When starting snort, I don't see anything about the portscan component
         Rules Engine: SF_SNORT_DETECTION_ENGINE  Version 1.17  <Build 18>           Preprocessor Object: SF_REPUTATION  Version 1.1  <Build 1>           Preprocessor Object: SF_MODBUS  Version 1.1  <Build 1>           Preprocessor Object: SF_GTP  Version 1.1  <Build 1>           Preprocessor Object: SF_SIP  Version 1.1  <Build 1>           Preprocessor Object: SF_DNP3  Version 1.1  <Build 1>           Preprocessor Object: SF_DCERPC2  Version 1.0  <Build 3>           Preprocessor Object: SF_SMTP  Version 1.1  <Build 9>           Preprocessor Object: SF_SSLPP  Version 1.1  <Build 4>           Preprocessor Object: SF_SSH  Version 1.1  <Build 3>           Preprocessor Object: SF_DNS  Version 1.1  <Build 4>           Preprocessor Object: SF_IMAP  Version 1.0  <Build 1>           Preprocessor Object: SF_POP  Version 1.0  <Build 1>           Preprocessor Object: SF_FTPTELNET  Version 1.2  <Build 13>           Preprocessor Object: SF_SDF  Version 1.1  <Build 1>Commencing packet processing (pid=9895)
Any help is appreciated ! 		 	   		  
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