Transcript Snort Intrusion Detection System

Snort
Intrusion Detection System
www.snort.org
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Outline
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What is snort?
What can it do?
How is it installed?
How is it configured?
How is it used?
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History
• First released in 1998 by Martin Roesch
• Originally intended to be a lightweight
intrusion detection technology.
• Has evolved ...
• 3 Million downloads
• 225k active users.
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Capabilities
• Four modes of operation
– Packet Sniffer mode
– Packet Logger mode
– Network Intrusion Detection Mode
– Network Intrusion Prevention
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Capabilities
• Packet Sniffer mode
– Read packets (based on rules) and display on
console
– ./snort -dev
• Packet Logger
– Log all packets into a local log, organized into
directories by IP address
– ./snort –dev –l ./log
– ./snort –dev –l ./log –h 192.168.1.0/24
Capabilities
• NIDS Mode
– Scan packets for a given combination of
parameters
– Output options – ASCII / binary (tcpdump
format)
– ./snort –d –l ./log –h 192.168.1.0/24 –c
snort.conf
Snort Rule
alert tcp any any -> $Home 80 (flags:S; msg:“Port 80 SYN”;)
• Action Field
– alert, log, pass, activate, dynamic
• Protocol Field
– tcp, udp, icmp, ip
• Source / Destination address and port
– direction indicator
• Rule Options
– msg, logto, id, dsize, seq, ack, flags, content, session
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Example Rules
alert tcp any any -> 192.168.5.0/24 21 \
(msg: “attempted anonymous ftp access”; \
content: “anonymous”; offset: 5;)
alert tcp any any -> any any (msg: “Null Scan”; \
flags: 0)
log tcp any any <> 192.168.5.0/24 21 \
(session: printable;)
alert udp any any -> 192.168.5.0/24 31337 \
(msg: “Back Orifice”;)
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Rule Types
• Alert Rules
• Pass Rules
• Log Rules
• Safe Order: Alert, Pass, Log
• Efficient Order: Pass, Alert, Log
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Installing Snort
• Locating the IDS relative to network
– Place Snort outside of firewall
– Place Snort just inside firewall
– Place Snort on critical systems (host based)
• Install software
– Download source or binaries from snort.org
• Windows / Linux
– Compile and/or install.
• /etc/snort (configuration files)
• /usr/sbin (executable program)
• /var/log/snort (typical log file directory)
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/etc/snort/snort.conf
• Serves as a default configuration
– (once home network has been identified)
• Data Types
– include (similar to programming includes)
• include: reference.config
– preprocessor (functional modules)
• preprocessor frag3
– var (variables)
• var HOME_NET 192.168.1.0/24
– config (configure various options)
• config disable_tcpopt_obsolete_alerts
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snort.conf setup
1) Set the variables for your network
2) Configure dynamic loaded libraries
3) Configure preprocessors
4) Configure output plugins
5) Add any runtime config directives
6) Customize your rule set
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snort.conf setup
• Set the variables for your network
– var HOME_NET [10.1.1.0/24,192.168.1.0/24]
– var EXTERNAL_NET any
– var DNS_SERVERS $HOME_NET
– var HTTP_SERVERS $HOME_NET
– var HTTP_PORTS 80
– var ORACLE_PORTS 1521
– var RULE_PATH /etc/snort/rules
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snort.conf setup
Configure dynamic loaded libraries
– Located in /usr/lib/snort2.x.x_dynamicpreprocessor
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libsf_dcerpc_preproc.so
libsf_dcerpc_preproc.so.0
libsf_dns_preproc.so
libsf_dns_preproc.so.0
libsf_ftptelnet_preproc.so
libsf_ftptelnet_preproc.so.0
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snort.conf setup
• Configure preprocessors
– preprocessor flow: stats_interval 0 hash 2
– preprocessor frag3_global: max_frags 65536
– preprocessor frag3_engine: policy first
detect_anomalies
– preprocessor stream4: disable_evasion_alerts
– preprocessor rpc_decode: 111 32771
– preprocessor bo
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snort.conf setup
Configure output plugins
– output alert_syslog: LOG_AUTH LOG_ALERT
– output database: log, mssql, dbname=snort \
user=snort password=test
– output alert_unified: filename snort.alert, limit 128
– ruletype suspicious
{
type log
output log_tcpdump: suspicious.log
}
– suspicious tcp $HOME_NET any -> $HOME_NET
6667 \ (msg:"Internal IRC Server";)
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snort.conf setup
• Add any runtime config directives
– config ignore_ports: tcp 21 6667:6671 1356
– config ignore_ports: udp 1:17 53
– config disable_decode_alerts
– config disable_tcpopt_obsolete_alerts
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snort.conf setup
• Customize your rule set
– include $RULE_PATH/local.rules
– include $RULE_PATH/bad-traffic.rules
– include $RULE_PATH/exploit.rules
– include $RULE_PATH/scan.rules
– include $RULE_PATH/finger.rules
– include $RULE_PATH/ftp.rules
• (More than 50 sets of rules defined)
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bad-traffic rules
• 12 rules in test rule set
• alert tcp $EXTERNAL_NET any <>
$HOME_NET 0 (msg:"BAD-TRAFFIC tcp
port 0 traffic"; flow:stateless;
classtype:misc-activity; sid:524; rev:8;)
– Capture any incoming traffic to port 0 of any
LAN HOME_NET machine.
– More information given in signature file 524.txt
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Signature 524.txt
Rule:
-Sid: 524
-Summary:
This event is generated when TCP traffic to port 0 is
detected. This should not be seen in normal TCP
communications.
-Impact:
Possible reconnaisance. This may be an attempt to verify
the existance of a host or hosts at a particular address
or address range.
-Detailed Information:
TCP traffic to port 0 is not valid under normal circumstances.
an indicator of unauthorized network use, reconnaisance
activity or system compromise. These rules may also
generate an event due to improperly configured
network devices.
-Affected Systems:
Any
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Attack Scenarios:
The attacker could send packets to a host with a destination
port of 0. The attacker might also be using hping to verify
the existance of a host as a prelude to an attack.
-Ease of Attack:
Simple
-False Positives:
None Known
-False Negatives:
None Known
-Corrective Action:
Disallow TCP traffic to port 0.
-Contributors:
Original rule writer unknown
Sourcefire Vulnerability Research Team
Nigel Houghton [email protected]
-Additional References:
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Certified Rules for Snort
• http://www.snort.org/pubbin/downloads.cgi
• Subscription User Rules
– Available immediately upon release
• Registered User Rules
– Same rules, but released with a 30 day delay
• Unregistered User Rules
– Single set of rules for each snort release
(mostly for testing purposes).
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Typical Installations
• Used in any of the configurations
discussed in IDS lecture
• Installation may be configured with several
Snort sensors
– outside network
– monitoring traffic just inside firewall
– monitoring key servers
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Inline Mode
• Configure Snort to receive packets from
iptables rather than libpcap.
• Separate capability that must be explicitly
installed.
• Adds 3 new rule types
– Drop –iptables drops packet and snort logs
– Reject – iptables rejects packet and snort logs
– Sdrop – iptables will drop packet. No logging.
Inline Mode
• Start iptables
– iptables –A OUTPUT –p tcp –dport –j QUEUE
– Traffic is routed to QUEUE, where it can be captured
by snort_inline
• Start Snort
– snort_inline –QDc ../etc/drop.conf –l /var/log/snort
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-Q – get packets from iptables
-D – run in daemon mode
-c – specify configuration file
-l – specify log file
Complex installations
• Use Snort to monitor traffic and log suspicious or
dangerous traffic.
• Store information in binary format
– Much faster than ascii storage.
• Store information to a database
– mysql, postgresql, oracle, MS sql, ODBC
– Much easier to process / analyze data
• Use data analysis front-ends to examine logs
– Barnyard (www.snort.org)
– BASE (Basic Analysis and Security Engine)
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Summary
• Snort is a powerful tool for monitoring
network traffic for anomalies that might
indicate network intrusion
• Can be used in several different
configurations
• Well supported
– Code Base
– Rules Sets
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