Transcript IDS: Intrusion Detection System C. Edward Chow 1

IDS: Intrusion Detection
System
C. Edward Chow
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Outline of The Talk
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Definition, Concepts
Network Intrusion Detection: Snort
A2D2 (Integrating NIDS with Firewall)
Host Intrusion Detection: Tripwire
References:
 Chapter 25 Intrusion Detection, by Matt Bishop.
 Chapter 7 Network Intrusion Detection, Inside Network Perimeter
Security, by Northcutt et al (reserved in UCCS Library)
 NIST IDS Survey: http://cs.uccs.edu/~chow/pub/ids/NISTsp800-31.pdf
 A2D2: http://cs.uccs.edu/~chow/pub/master/acearns/doc/
 http://cs.uccs.edu/~chow/pub/ids/2001_vigna_kemmerer_blix_raid01.p
df
 Snort: http://www.snort.org/
 Tripwire: http://www.tripwire.org/
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Architecture of IDS
HIDS: Host Intrusion Detection System
NIDS: Network Intrusion Detection System
(logger)
HOST A
HIDS
HOST A
HIDS
Director
(Analyzer)
HOST A
NIDS
HOST A
HIDS
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HIDS vs. NIDS
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Two Basic Types of IDS:
Host-based IDS:
 Periodically analyze logs, perform file system integrity check.
 Examples:
– Generic: ISS RealSecure Server Sensor.
– Check host file system: Tripwire, AIDE
– Check host network connections: BlackICE, PortSentry
– Check host’s log files: LogSentry, Swatch
Network-based IDS:
 Analyze network traffic content and pattern for signs of intrusion
 Examples:
– Snort, Cisco IDS4235,
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DMZ
IDS Placement
DNS
Mail
Web
Server Server Server
IDS
Internet
Firewall
Router
Outer Firewall
SW
IDS
IDS
Firewall
SW
Inner Firewall
Intra1
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Snort
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A popular network intrusion public domain package, available on
www.snort.org.
It allows the user to specify a set of rules which specifies the pattern
in the packets, and the corresponding actions (typically just an alert
msg) for matched packets.
It also allows the user to create their own plug-in for additional
detection that is not available with default pattern matching. For
example, the subnet flooding, it requires modification of
preprocessing step.
It was used by many other packages and products.
On snort download site, installation steps are given for integrating
snort with mysql, apache, webmin, and ACID for easy web-based
access and display of the intrusion instance, statistics, and related
intrusion event databases, such as CVE, arachNIDS.
See http://www.snort.org/docs/snort-rh7-mysql-ACID-1-5.pdf for
more details.
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Snort-based
IDS
Setup Example
(from Steven Scott’s
tutorial)
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Basic Snort Usage
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Snort has three main modes:
 Sniffer mode: read packets and display on console.
– E.g., >Snort -dev
– v: verbose; d: dump application data data; e: extensive
 Packet Logger: read packets and log to the disk.
– E.g., > snort –dev –l ./log –h 192.168.1.0/24
– l: log, h: only capture packets relative to the host
 NIDS: analyze packets and matched against user defined rules and perform actions.
– E.g., > snort –dev –l ./log –c snort.conf
– add –D will have snort run as daemon.
– -A [fast | full | unsock | non]
– -b for binary (tcpdump) format; faster.
Use –r snort.og to read it back for offline analysis.
– -o: change the normal (alertpasslog rules) processing order to (passalertlog).
– You can use SMB alert. That use smbclient to send WinPopup alert msg to window
machines.
– Use –O for (obsuscates) the ip addresses in log file for hiding IP addresses when
sharing with others the logs.
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/etc/snort/snort.conf
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Snort read the snort.conf file for the default variables, additional pre/post
processing plug-in (if any), output specification (to a mysql for example),
and a set of rule files. For example,
http://cs.uccs.edu/~chow/pub/snort/snort.conf
output database: log, mysql, user=snort password=xxxx dbname=snort
host=localhost
include bad-traffic.rules
include exploit.rules
include scan.rules
include finger.rules
include ftp.rules
include telnet.rules
include rpc.rules
include rservices.rules
include dos.rules
include ddos.rules
include dns.rules
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Snort Rule Syntax
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Most rules written in single line. If multiple line use \
Each snort rule has two logical section: rule header and rule options.
alert icmp $EXTERNAL_NET any <> $HOME_NET any (msg:"DDOS
Stacheldraht agent->handler (skillz)"; content:"skillz"; itype:0;
icmp_id:6666;
reference:url,staff.washington.edu/dittrich/misc/stacheldraht.analysis;
classtype:attempted-dos; sid:1855; rev:2;)
alert any any -> 192.168.1.0/24 any (flags:A; ack:0; msg: “NMAP TCP
ping”;)
# nmap send TCP ACK pkt with ack field set to 0
alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS
(msg:"WEB-IIS cmd.exe access"; flow:to_server,established;
content:"cmd.exe"; nocase; classtype:web-application-attack; sid:1002;
rev:5;)
Rule header contains action, protocol, source (IPaddr/port), direction,
destination (IPaddr/port)
Rule option contains alert msgs, info on which parts of packet to be
inspected.
-> and <> are the only two direction operators.
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Snort Rule Syntax
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Var: <name> <value>
var: EXTERNAL_NET [128.198.160.0/19, 128.198.61.0/26]
var: HOME_LAN [192.168.0.0/24, 10.1.1,0/24]
var NON_WIRELESS !128.198.61.128/25
# use ! for negative operator for specifying the CIDR address not within a range.
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Use $<variable> to reference them later.
alert tcp $EXTERNAL_NET any  $HOME_LAN any (flags: S; msg: “SYN packet”;)
Rule Actions:
 Alert
 Log
 Pass (ignore the packet)
 Activate (alert then turn on another dynamic rule (being phase out)
 Dynamic– remain idle until activated by an activeate rule, then act as a log rule.
You can also define your own rule types. Then use it as rule actioin.
ruletype redalert {
type
alert output
alert_syslog
LOG_AUTH LOG_ALERT
output database: log, mysql,user=snort dbname=snort host=localhost
}
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Rule option: Content
content: [!] “<content string>”;
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It allows the user to set rules that search for specific content in
packet payload and trigger response based on the data.
Case sensitive. Can be mixed text and binary.
Use | to specify the byte code (hexadecimal number).
! For negation; nocase to make case-insensitive matching.
Examples:
 Alert tcp any any -> 192.168.1.0/24 143 (content: “|90CB C0FF
FFFF|/bin/sh”;\
msg: “IMAP buffer overflow!”)
 Alert tcp any any -> 192.168.1.0/24 21 (content: !”GET”; depth:
3; nocase; \
dsize: >100; msg: “Long Non-Get FTP command!”)
 Dsize: payload size.
Related IMAP buffer overflow,
http://www.securityfocus.com/bid/130/discussion/
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Rule option: offset and depth
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Offset: < number>
Specify the number of bytes to skip before starting
pattern matching.
Depth: <number>
Set maximum search depth for content pattern match.
alert tcp any any -> $HLAN 80
(content: “cmd.exe”; offset: 3; depth: 22: msg: “com.exe
attack”;)
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Rule option: sid & flow
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Sid specifies unique snort rule.
<100 reserved for future use.
100-1,000,000 rule included in snort distirbution.
>1,000,000 for local rule usage.
Flow: use in conjunction with TCP stream reassembly.
Option: to_server (client request), to client (server
response), from_client, from_server.
E.g., alert tcp $EXTERNAL_NET any ->
$HTTP_SERVERS $HTTP_PORTS (msg:"WEB-IIS
cmd.exe access"; flow:to_server,established;
content:"cmd.exe"; nocase; classtype:web-applicationattack; sid:1002; rev:5;)
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Detection Results
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#0-(3-1)
21:14:00
[snort] WEB-IIS cmd.exe access
2003-04-14
65.106.21.153:1541
128.198.161.110:80
TCP
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C:\work\cucs\cs691\S2003>nslookup 65.106.21.153
Server: evans.eas.uccs.edu
Address: 128.198.160.66
Name: diahost153.dia.cnc.net
Address: 65.106.21.153
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Detection Results
ID < Signature > < Timestamp > < Source Address > < Dest. Address > < Layer 4 Proto >
#0-(4-39)
#1-(4-38)
#2-(4-37)
#3-(4-36)
#4-(4-35)
#5-(4-34)
#6-(4-33)
#7-(4-32)
#8-(4-31)
[snort] SCAN Proxy (8080) attempt
2003-04-1619:11:51
128.198.161.110:63906
128.198.61.61:8080
TCP
[snort] SCAN Proxy (8080) attempt
2003-04-16 19:11:51
128.198.161.110:63905
128.198.61.61:8080
TCP
[cve][icat][cve][icat][snort] SNMP AgentX/tcp request
2003-04-16 19:11:49
128.198.161.110:63906
128.198.61.61:705
[cve][icat][cve][icat][snort] SNMP AgentX/tcp request
2003-04-16 19:11:49
128.198.161.110:63905
128.198.61.61:705
url[snort] SCAN SOCKS Proxy attempt
2003-04-16 19:11:48
128.198.161.110:63906
128.198.61.61:1080
TCP
url[snort] SCAN SOCKS Proxy attempt
2003-04-16 19:11:48
128.198.161.110:63905
128.198.61.61:1080
TCP
[cve][icat][cve][icat][snort] SNMP request tcp
2003-04-16 19:11:30
128.198.161.110:63906
128.198.61.61:161
TCP
[cve][icat][cve][icat][snort] SNMP request tcp
2003-041619:11:29
128.198.161.110:63905
128.198.61.61:161
TCP
[snort] SCAN Squid Proxy attempt
2003-04-16 19:11:27
128.198.161.110:63906
128.198.61.61:3128
TCP
#9-(4-30)
[snort] SCAN Squid Proxy attempt
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2003-04-16 19:11:27
128.198.161.110:63905
18
128.198.61.61:3128
TCP
TCP
TCP
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False Positives vs False Negatives
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False positives: something occurs that causes IDS to
incorrectly identify an intrusion when none has occurred.
False negatives: something occurs that causes IDS to
incorrectly fail to identify an intrustion when one has in
fact occurred.
Accuracy of IDS: reflect the number of false positives.
Completeness: reflect the number of false negatives.
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Attack Response Rules
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Check on the responses of server for obvious pattern that the system has be
attacked/compromised.
https://128.198.61.61:10000/snort/conf_rules.cgi?rule=attack-responses
Examples:
alert tcp $HTTP_SERVERS $HTTP_PORTS -> $EXTERNAL_NET any
(msg:"ATTACK RESPONSES index of /cgi-bin/ response";
flow:from_server,established; content:"Index of /cgi-bin/"; nocase; classtype:badunknown; sid:1666; rev:3;)
alert tcp $HOME_NET 22 -> $EXTERNAL_NET any (msg:"ATTACK-RESPONSE
successful gobbles ssh exploit (GOBBLE)"; flow:from_server,established;
content:"|2a|GOBBLE|2a|"; reference:bugtraq,5093; classtype:successful-admin;
sid:1810; rev:2;)
http://www.securityfocus.com/bid/5093
alert tcp $HOME_NET 749 -> $EXTERNAL_NET any (msg:"ATTACK-RESPONSE
successful kadmind bufferflow attempt"; flow:established,from_server;
content:"*GOBBLE*"; depth:8; reference:cve,CAN-2002-1235;
reference:url,www.kb.cert.org/vuls/id/875073; classtype:successful-admin; sid:1900;
rev:1;)
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BackDoor Trojan
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Try to detect know ports and content of packet that are
used and generated by the backdoor trojan.
alert tcp $HOME_NET 6789 -> $EXTERNAL_NET any
(msg:"BACKDOOR Doly 2.0 access"; content: "|57 74
7a 75 70 20 55 73 65|"; flags: A+; depth: 32;
reference:arachnids,312; sid:119; classtype:miscactivity; rev:3;)
http://www.whitehats.com/cgi/arachNIDS/Show?_id=ids
312&view=research
https://128.198.61.61:10000/snort/conf_rules.cgi?rule=b
ackdoor
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DDoS Rules
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DDoS with know protocol/port/content.
https://128.198.61.61:10000/snort/conf_rules.cgi?rule=ddos
alert icmp $EXTERNAL_NET any <> $HOME_NET any
(msg:"DDOS Stacheldraht handler->agent (ficken)";
content:"ficken"; itype:0; icmp_id:6667;
reference:url,staff.washington.edu/dittrich/misc/stacheldraht.analysi
s; classtype:attempted-dos; sid:1856; rev:2;)
alert udp $EXTERNAL_NET any -> $HOME_NET 31335
(msg:"DDOS Trin00\:DaemontoMaster(PONGdetected)";
content:"PONG";reference:arachnids,187; classtype:attemptedrecon; sid:223; rev:1;)
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DNS rules
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Zone transfer, DNS buffer overflow exploit.
https://128.198.61.61:10000/snort/conf_rules.cgi?rule=dns
alert tcp $EXTERNAL_NET any -> $DNS_SERVERS 53
(msg:"DNS zone transfer TCP"; flow:to_server,established; content:
"|00 00 FC|"; offset:14; reference:cve,CAN-1999-0532;
reference:arachnids,212; classtype:attempted-recon; sid:255;
rev:7;)
alert tcp $EXTERNAL_NET any -> $DNS_SERVERS 53
(msg:"DNS EXPLOIT x86 linux overflow attempt (ADMv2)";
flow:to_server,established; content:"|89f7 29c7 89f3 89f9 89f2 ac3c
fe|"; classtype:attempted-admin; sid:265; rev:3;)
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Scan rules
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Scan certain node/ports. (network scan vs port scan)
https://128.198.61.61:10000/snort/conf_rules.cgi?rule=scan
alert tcp $EXTERNAL_NET any -> $HOME_NET 3128
(msg:"SCAN Squid Proxy attempt"; flags:S; classtype:attemptedrecon; sid:618; rev:2;)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN
synscan portscan"; id: 39426; flags: SF;reference:arachnids,441;
classtype:attempted-recon; sid:630; rev:1;)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN
nmap TCP";flags:A;ack:0; reference:arachnids,28;
classtype:attempted-recon; sid:628; rev:1;)
alert icmp $EXTERNAL_NET any -> $HOME_NET any
(msg:"SCAN SolarWinds IP scan attempt";
content:"SolarWinds.Net"; itype:8; icode:0; classtype:network-scan;
sid:1918; rev:3;)
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WEB-CGI Rules
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https://128.198.61.61:10000/snort/conf_rules.cgi?rule=web-cgi
alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS
$HTTP_PORTS (msg:"WEB-CGI perl.exe access";
flow:to_server,established; uricontent:"/perl.exe"; nocase;
reference:cve,CAN-1999-0509;
reference:url,www.cert.org/advisories/CA-1996-11.html;
reference:arachnids,219; reference:nessus,10173;
classtype:attempted-recon; sid:832; rev:8;)
.. (DOT DOT) ATTACK.
alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS
$HTTP_PORTS (msg:"WEB-CGI technote main.cgi file directory
traversal attempt"; flow:to_server,established;
uricontent:"/technote/main.cgi"; nocase; content:"filename=";
nocase; content:"../../"; reference:cve,CVE-2001-0075;
reference:bugtraq,2156; classtype:web-application-attack; sid:1051;
rev:7;)
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WEB-IIS Rules
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https://128.198.61.61:10000/snort/conf_rules.cgi?rule=w
eb-iis
alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS
$HTTP_PORTS (msg:"WEB-IIS unicode directory
traversal attempt"; flow:to_server,established;
content:"/..%c0%af../"; nocase; classtype:webapplication-attack; reference:cve,CVE-2000-0884;
sid:981; rev:6;)
alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS
$HTTP_PORTS (msg:"WEB-IIS cmd.exe access";
flow:to_server,established; content:"cmd.exe"; nocase;
classtype:web-application-attack; sid:1002; rev:5;)
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SMTP Rules
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SMTP has quite a few buffer overlfow exploit.
https://128.198.61.61:10000/snort/conf_rules.cgi?rule=smtp
alert tcp $EXTERNAL_NET any -> $SMTP_SERVERS 25 (msg:"SMTP
RCPT TO overflow"; flow:to_server,established; content:"rcpt to|3a|";
nocase; content:!"|0a|"; within:800; reference:cve,CAN-2001-0260;
reference:bugtraq,2283; classtype:attempted-admin; sid:654; rev:7;)
alert tcp $EXTERNAL_NET any -> $SMTP_SERVERS 25 (msg:"SMTP
sendmail 5.6.5 exploit"; flow:to_server,established; content:"MAIL
FROM|3a207c|/usr/ucb/tail"; nocase; reference:arachnids,122;
classtype:attempted-user; sid:665; rev:4;)
alert tcp $EXTERNAL_NET any -> $SMTP_SERVERS 25 (msg:"SMTP
From comment overflow attempt"; flow:to_server,established;
content:"From\:";
content:"<><><><><><><><><><><><><><><><><><><><><><>";
distance:0; content:"("; distance:1; content:")"; distance:1;
reference:cve,CAN-2002-1337;
reference:url,www.kb.cert.org/vuls/id/398025; classtype:attempted-admin;
sid:2087; rev:2;)
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Bad Traffic
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Bad packet header content
https://128.198.61.61:10000/snort/conf_rules.cgi?rule=b
ad-traffic
alert tcp $EXTERNAL_NET any -> $HOME_NET any
(msg:"BAD TRAFFIC data in TCP SYN packet"; flags:S;
dsize:>6; reference:url,www.cert.org/incident_notes/IN99-07.html; sid:526; classtype:misc-activity; rev:4;)
alert ip any any -> any any (msg:"BAD TRAFFIC same
SRC/DST"; sameip; reference:cve,CVE-1999-0016;
reference:url,www.cert.org/advisories/CA-1997-28.html;
classtype:bad-unknown; sid:527; rev:3;)
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HIDS: Host-based Intrusion Detection
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Detect and examine malicious activity (same as
network-based intrusion detection.)
 Optimize for monitoring individual hosts.
 Monitor system network activity, file system, log files,
user actions.
 Integrate the finding of several host-based intrusion
detection provide unified view of multiple systems in the
network.
 Detect escalation of privileges for a user or system
account. (from guest user to have admin privilege).
 NIDS can not usually see or interpret such actions
which takes place on a host.
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HIDS’ Advantages over NIDS
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HIDS can monitor user-specific activity of the system
 Check process listing, local log files, system calls.
 It is difficult for NIDS to associate packets to specific users
(except when content switch-based NIDS is used!) and to
determine if the commands in the packets violate specific user’s
access privilege.
HIDS sensor can monitor encrypted traffic by tapping in at the
connection endpoint such as VPN connection. (NIDS can not check
encrypted IPsec/SSL payload.)
HIDS can help detect attack that evade NIDS detection.
For example, attacks encode dangerous commands in nonstandard Unicode encoding. checking for ".ida". An example
request would look like: GET /himom.id%u0061 HTTP/1.0
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Tripwire: A Host-based IDS
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Original version developed at Purdue Univ. 1992 by Dr. Eugene
Spafford and Gene Kim, now CTO of Tripwire
http://www.tripwire.org/downloads/index.php Linux public domain
software download. http://www.tripwire.org/qanda/faq.php
Commercial evaluation version tripwire3.0 (with manager and
server, run on both Linux/windows) available at
http://www.tripwire.com/downloads/
 Tripwire managers provide gui and unified interface to monitor
multiple instances of tripwire program.
 Can monitor configuration of routers/switches.
 Here is a presentation from tripwire.com.
There is Advanced Intrusion Detection Environment (AIDE)
available at http://www..cs.tut.fi/~rammer/aide.html. It is actively
maintained and developed. Not on windows. Does not encrypt and
sign the baseline datagbase. (The tripwire does this).
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File Access Permission Change
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Example of Policy File
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For windows systems,
http://cs.uccs.edu/~cs691/tripwire/windows/Policy/twpol.
txt
For linux,
http://cs.uccs.edu/~cs691/tripwire/linux/Policy/twpol.txt
http://cs.uccs.edu/~cs691/tripwire/windows/Documents/r
eference_guide.pdf page 25.
Rule: object -> properties;
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