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An Introduction to Snort

An Introduction to Snort. Richard Bejtlich TaoSecurity Houston ISSA Meeting 11 Apr 02. Outline. Introduction to Intrusion Detection What is Snort? Installing Snort Snort Rules Snort in Action Third-Party Enhancements Conclusion. About Me. Bejtlich = “bate-lik”

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An Introduction to Snort

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  1. An Introduction to Snort Richard Bejtlich TaoSecurity Houston ISSA Meeting 11 Apr 02

  2. Outline • Introduction to Intrusion Detection • What is Snort? • Installing Snort • Snort Rules • Snort in Action • Third-Party Enhancements • Conclusion

  3. About Me • Bejtlich = “bate-lik” • Senior engineer for managed network security operations, BATC (2001-) • Former captain at US Air Force Computer Emergency Response Team (1998-2001) • Student of intrusion detection, incident response, and digital forensics • www.taosecurity.com

  4. Introduction to Intrusion Detection • Network defense or “protection” model • Planning • Prevention • Detection • Response • Intrusion detection is the process of discovering, analyzing, and reporting unauthorized or damaging network or computer activities

  5. Introduction to Intrusion Detection • All network and computer activities fall in one of three categories: • Normal • Abnormal but not malicious • Malicious • Intrusion detection operates in two arenas: • What a computer says: network traffic • What a computer thinks: computer processes

  6. Introduction to Intrusion Detection • Network traffic is monitored by network-based intrusion detection systems (NIDS) • Computer processes are monitored by host-based intrusion detection systems (HIDS) • So-called “hybrid” systems examine network traffic to or from a host, as well as processes on that host • NIDS are easier to deploy and manage, but HIDS may give greater visibility to events

  7. What is Snort? • Snort is a fast, flexible, small-footprint, open-source NIDS developed by the security community and a “benevolent dictator” • Lead coder: Marty Roesch, now founder of Sourcefire (www.sourcefire.com) • Initially developed in late 1998 as a sniffer with consistent output, unlike protocol-dependent output of TCPDump • Licensed under GPL, but version 2.0 may change to a different license

  8. Installing Snort • As of 16 Mar 02, version 1.8.4 available at www.snort.org/dl/ in these forms: • UNIX source • Solaris, FreeBSD, Windows binary packages • Red Hat .rpm • Requires installation of libpcap first! • UNIX: www.tcpdump.org/release/libpcap-0.7.1.tar.gz or newest available source • Windows: netgroup-serv.polito.it/winpcap/install/ offers winpcap 2.2 and 2.3 beta (XP requires 2.3)

  9. Installing Snort • On Red Hat Linux 7.2, as root: • Download and install libpcap • Download and install these three .rpm: • libnet-1.0.2a-1snort.i386.rpm • snort-1.8.4-1snort.i386.rpm • snort-postgresql+flexresp-1.8.4-1snort.i386.rpm • Create /var/log/snort directory • Files installed: • /etc/snort contains conf and rule files • /var/log/snort will contain logs • /usr/sbin/snort contains snort binary

  10. Installing Snort • For a quick test, execute this command within the /etc/snort directory: • snort –A console • From a separate machine, use nmap to generate events for Snort to detect: • nmap –sP <snort_machine_IP_address> • You should see an alert like this: 03/27-15:18:06.911226 [**] [1:469:1] ICMP PING NMAP [**] [Classification: Attempted Information Leak] [Priority: 2] {ICMP} 192.168.1.20 -> 192.168.1.237

  11. Installing Snort • On Windows 2000, as administrator: • Download and install winpcap • Download and execute Snort184Win32.exe, and select “typical” installation • mkdir “c:\Program Files\Sourcefire\Snort\log” • Files installed in c:\Program Files\Sourcefire\Snort: • snort.conf • \rules directory contains rules • snort.exe executable

  12. Installing Snort • To test, execute this command within the c:\Program Files\Sourcefire\Snort directory: • snort –A console • You may need to specify and interface with ‘-i 2’ • From a separate machine, use nmap to generate events for Snort to detect: • nmap –sP <snort_machine_IP_address> • You should see an alert like this: 03/27-15:18:06.911226 [**] [1:469:1] ICMP PING NMAP [**] [Classification: Attempted Information Leak] [Priority: 2] {ICMP} 192.168.1.20 -> 192.168.1.237

  13. Installing Snort • While not an element of Snort, Ethereal is the best open source GUI-based packet viewer • www.ethereal.com offers: • Windows: www.ethereal.com/distribution/win32/ethereal-setup-0.9.2.exe • UNIX: www.ethereal.com/download.html • Red Hat Linux RPMs: ftp.ethereal.com/pub/ethereal/rpms/

  14. Installing Snort • Also not an element of Snort, tcpdump is a well-established CLI packet capture tool • www.tcpdump.org offers UNIX source • netgroup-serv.polito.it/windump/install/ offers windump, a Windows port of tcpdump • windump is helpful because it will help you see the different interfaces available on your sensor • Next slide shows two available interfaces; note only the second is capable of sniffing • snort –A console –i 2

  15. Snort Rules • Snort rules are extremely flexible and are easy to modify, unlike many commercial NIDS • Sample rule to detect SubSeven trojan: alert tcp $EXTERNAL_NET 27374 -> $HOME_NET any (msg:"BACKDOOR subseven 22"; flags: A+; content: "|0d0a5b52504c5d3030320d0a|"; reference:arachnids,485; reference:url,www.hackfix.org/subseven/; sid:103; classtype:misc-activity; rev:4;) • Elements before parentheses comprise ‘rule header’ • Elements in parentheses are ‘rule options’

  16. Snort Rules alert tcp $EXTERNAL_NET 27374 -> $HOME_NET any (msg:"BACKDOOR subseven 22"; flags: A+; content: "|0d0a5b52504c5d3030320d0a|"; reference:arachnids,485; reference:url,www.hackfix.org/subseven/; sid:103; classtype:misc-activity; rev:4;) • alert action to take; also log, pass, activate, dynamic • tcp protocol; also udp, icmp, ip • $EXTERNAL_NET source address; this is a variable – specific IP is ok • 27374 source port; also any, negation (!21), range (1:1024) • -> direction; best not to change this, although<>is allowed • $HOME_NET destination address; this is also a variable here • any destination port

  17. Snort Rules alert tcp $EXTERNAL_NET 27374 -> $HOME_NET any (msg:"BACKDOOR subseven 22"; flags: A+; content: "|0d0a5b52504c5d3030320d0a|"; reference:arachnids,485; reference:url,www.hackfix.org/subseven/; sid:103; classtype:misc-activity; rev:4;) • msg:”BACKDOOR subseven 22”; message to appear in logs • flags: A+; tcp flags; many options, like SA, SA+, !R, SF* • content: “|0d0…0a|”;binary data to check in packet; content without | (pipe) characters do simple content matches • reference…;where to go to look for background on this rule • sid:103;rule identifier • classtype: misc-activity;rule type; many others • rev:4;rule revision number • other rule options possible, like offset, depth, nocase

  18. Snort Rules • bad-traffic.rules exploit.rules scan.rules • finger.rules ftp.rules telnet.rules • smtp.rules rpc.rules rservices.rules • dos.rules ddos.rules dns.rules • tftp.rules web-cgi.rules web-coldfusion.rules • web-frontpage.rules web-iis.rules web-misc.rules • web-attacks.rules sql.rules x11.rules • icmp.rules netbios.rules misc.rules • backdoor.rules shellcode.rules policy.rules • porn.rules info.rules icmp-info.rules • virus.rules local.rules attack-responses.rules

  19. Snort Rules • Rules which actually caught intrusions • alert tcp $EXTERNAL_NET any -> $SQL_SERVERS 1433 (msg:"MS-SQL xp_cmdshell - program execution"; content: "x|00|p|00|_|00|c|00|m|00|d|00|s|00|h|00|e|00|l|00|l|00|"; nocase; flags:A+; classtype:attempted-user; sid:687; rev:3;)caught compromise of Microsoft SQL Server • alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS 80 (msg:"WEB-IIS cmd.exe access"; flags: A+; content:"cmd.exe"; nocase; classtype:web-application-attack; sid:1002; rev:2;) caught Code Red infection • alert tcp $EXTERNAL_NET any -> $HOME_NET 21 (msg:"INFO FTP \"MKD / \" possible warez site"; flags: A+; content:"MKD / "; nocase; depth: 6; classtype:misc-activity; sid:554; rev:3;) caught anonymous ftp server

  20. Snort Rules • More rules that caught intrusions • alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS 80 (msg:"WEB-IIS multiple decode attempt"; flags:A+; uricontent:"%5c"; uricontent:".."; reference:cve,CAN-2001-0333; classtype:web-application-attack; sid:970; rev:2;) caught NIMDA infection • alert tcp $HOME_NET 23 -> $EXTERNAL_NET any (msg:"TELNET Bad Login"; content: "Login incorrect"; nocase; flags:A+; classtype:bad-unknown; sid:1251; rev:2;) caught telnet username brute-force • Consider how a rule with “Login incorrect” might trigger on many non-malicious events

  21. Snort in Action • Three operational modes: • Sniffer: snort –dvae will be display payloads, be verbose, display arp traffic, and display link layer data • Packet logger: snort –b –l /var/log/snortwill log binary data to the /var/log/snort directory • NIDS: snort –b –l /var/log/snort –A full –c /etc/snort/snort.confwill log binary data in the /var/log/snort directory, with full alerts in /var/log/snort/alert, reading the configuration file in /etc/snort

  22. Snort in Action • Three ways to tell Snort how to act • snort.conf configures variables, preprocessors, output plugins, and active rule sets • .rules files define actual signatures • Command line options start snort and will override options in snort.conf file • Snort will run with default snort.conf, but you will have less ‘chaff’ to sort through if you spend time configuring snort.conf properly

  23. Snort in Action • Snort as NIDS (third mode) captures recon • Contents of /var/log/snort/alert [**] [1:469:1] ICMP PING NMAP [**][Classification: Attempted Information Leak] [Priority: 2]03/28-09:48:40.739935 192.168.1.2 -> 192.168.1.3ICMP TTL:46 TOS:0x0 ID:61443 IpLen:20 DgmLen:28Type:8 Code:0 ID:10629 Seq:0 ECHO[Xref => http://www.whitehats.com/info/IDS162] [**] [1:469:1] spp_portscan: PORTSCAN DETECTED from 192.168.1.2 (THRESHOLD 4 connections exceeded in 0 seconds) [**]03/28-09:48:41.052635 [**] [100:2:1] spp_portscan: portscan status from 192.168.1.2: 183 connections across 1 hosts: TCP(183), UDP(0) [**]03/2809:48:45.007501

  24. Snort in Action • Partial contents of /var/log/snort/portscan.log Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:106 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:193 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:138 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:128 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:156 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:35 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:48 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:16 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:173 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:72 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:65 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:36 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:149 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:17 SYN ******S* Mar 28 09:48:41 192.168.1.2:45061 -> 192.168.1.3:218 SYN ******S*

  25. Snort in Action • /var/log/snort/snort-0328\@0948.log is in binary format; read with Ethereal or tcpdump • Sample tcpdump output of this log file 09:48:40.739935 192.168.1.2 > 192.168.1.3: icmp: echo request 09:48:40.743705 192.168.1.2 > 192.168.1.3: icmp: echo request • As configured, Snort will only log the packets which triggered an alert • Packets triggering portscans are not logged by default

  26. Third-Party Enhancements • SnortSnarf • www.silicondefense.com/software/snortsnarf/ • SnortSnarf is a Perl program to take files of alerts from the Snort to produce HTML reports • Output intended for diagnostic inspection • Silicon Defense also supplies sensors with commercial support • Description and screenshot taken from SnortSnarf web

  27. Third-Party Enhancements • Analysis Console for Intrusion Databases (ACID) • acidlab.sourceforge.net/ • PHP-based analysis engine to search and process a database of security events generated by various IDSes, firewalls, and network monitoring tools • Query-builder and search interface, packet viewer (decoder), alert management, chart and statistics generation • Description and screenshots taken from ACID web

  28. Demarc • www.demarc.com • NIDS management console, integrating Snort with the convenience and power of a centralized interface for all network sensors • Monitor all servers / hosts to make sure network services such as a mail or web servers remain accessible at all times • Monitor system logs for anomalous log entries that may indicate intruders or system malfunctions • Description and screenshots taken from demarc web

  29. Conclusion • Snort is a powerful tool, but maximizing its usefulness requires a trained operator • Becoming proficient with network intrusion detection takes 12 months; “expert” 24-36? • Snort is considered a superior NIDS when compared to most commercial systems • Managed network security providers should collect enough information to make decisions without calling clients to ask what happened

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