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KULIAH III
THREAT AND ATTACK (2)
Aswin Suharsono
KOM 15008
Keamanan Jaringan
2012/2013
Overview
• Phase 3: Gaining Access Using Network Attacks
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Sniffing
IP Address Spoofing
Session Hijacking
Netcat
DOS
• Phase 4: Maintain Access
– Trojan
– Backdoors
• Phase 5 Covering Tracks and Hiding
Sniffer
• Allows attacker to see everything sent across the
network, including userIDs and passwords
• NIC placed in promiscuous mode
• Tcpdump http://www.tcpdump.org
• Windump http://netgroup-serv.polito.it/windump
• Snort http://www.snort.org
• Ethereal http://www.ethereal.com
• Sniffit
http://reptile.rug.ac.be/~coder/sniffit/sniffit.html
• Dsniff http://www.monkey.org/~dugsong/dsniff
Passive Sniffers
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Sniffers that passively wait for traffic to be sent to them
Well suited for hub environment
Snort
Sniffit
Figure 8.2 A LAN implemented with a hub
Bad guys can sniff packets
packet “sniffing”:
– broadcast media (shared ethernet, wireless)
– promiscuous network interface reads/records all
packets (e.g., including passwords!) passing by
C
A
src:B dest:A
payload

B
wireshark software used for end-of-chapter labs is a (free)
packet-sniffer
Introduction
1-6
Bad guys can use fake addresses
IP spoofing: send packet with false source
address
C
A
src:B dest:A
payload
B
… lots more on security (throughout, Chapter 8)
Introduction
1-7
• Ethereal
• Gunakan switch, jangan hub
IP Address Spoofing
• Changing or disguising the source IP address
• used by Nmap in decoy mode
• Used by Dsniff in dnsspoof attack
– DNS response sent by Dsniff contains source address of the DNS
server
• Used in denial-of-service attacks
• Used in undermining Unix r-commands
• Used with source routing attacks
Simple IP Address Spoofing
• Pros
– Works well in hiding source of a packet flood or other denial-ofservice attack
• Cons
– Difficult for attacker to monitor response packets
– Any response packet will be sent to spoofed IP address
– Difficult to IP address spoof against any TCP-based service unless
machines are on same LAN and ARP spoof is used
Figure 8.13 The TCP three-way handshake inhibits
simple spoofing
Figure 8.14 Bob trusts Alice
Figure 8.15 Everyone trusts Alice, the administrator’s
main management system
Session Hijacking
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•
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•
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Session Hijacking, Perpaduan antara Sniffing dan Spoofing
Pengertian Session
Sniff for session
Rekam
Gunakan untuk masuk
Dengan mencuri Session milik orang lain, maka bisa masuk
tanpa perlu login
Bad guys: attack server, network
infrastructure
Denial of Service (DoS): attackers make resources (server, bandwidth)
unavailable to legitimate traffic by overwhelming resource with bogus
traffic
1. select target
2. break into hosts around the
network (see botnet)
3. send packets to target from
compromised hosts
target
Introduction
1-16
SYN Flood
• Attacker sends continuous stream of SYN packets to target
• Target allocates memory on its connection queue to keep track of
half-open connections
• Attacker does not complete 3-way handshake, filling up all slots on
connection queue of target machine
• If target machine has a very large connection queue, attacker can
alternatively send sufficient amount of SYN packets to consume
target machine’s entire network bandwidth
Smurf Attacks
• Aka directed broadcast attacks
• Smurf attacks rely on an ICMP directed broadcast to create a
flood of traffic on a victim
• Attacker uses a spoofed source address of victim
• Smurf attack is a DOS that consumes network bandwidth of
victim
• Smurf amplifier is a network that responds to directed broadcast
messages
4. Maintaining Access
Trojan Horses
• Software program containing a concealed malicious
capability but appears to be benign, useful, or attractive
to users
Backdoor
• Software that allows an attacker to access a machine using an
alternative entry method
• Installed by attackers after a machine has been compromised
• May Permit attacker to access a computer without needing to
provide account names and passwords
• Used in movie “War Games”
• Can be sshd listening to a port other than 22
• Can be setup using Netcat
Netcat as a Backdoor
• A popular backdoor tool
• Netcat must be compiled with “GAPING_SECURITY_HOLE”
option
• On victim machine, run Netcat in listener mode with –e flag to
execute a specific program such as a command shell
• On attacker’s machine run Netcat in client mode to connect to
backdoor on victim
Traditional RootKits
• A suite of tools that allow an attacker to maintain
root-level access via a backdoor and hiding
evidence of a system compromise
• More powerful than application-level Trojan horse
backdoors(eg. BO2K, Netcat) since the latter run
as separate programs which are easily detectable
• a more insidious form of Trojan horse backdoor
than application-level counterparts since existing
critical system components are replaced to let
attacker have backdoor access and hide
Kernel-Level RootKits
• More sinister, devious, and nasty than traditional RootKits
• Operating system kernel replaced by a Trojan horse kernel that appears to be
well-behaved but in actuality is rotten to the core
• Critical system files such as ls, ps, du, ifconfig left unmodified
• Trojanized kernel can intercept system calls and run another application
chosen by atttacker
– Execution request to run /bin/login is mapped to /bin/backdoorlogin
– Tripwire only checks unaltered system files
• If the kernel cannot be trusted, nothing on the system can be trusted
5. Covering Tracks
Hiding Evidence by
Altering Event Logs
• Attackers like to remove evidence from logs associated with
attacker’s gaining access, elevating privileges,and installing
RootKits and backdoors
– Login records
– Stopped and restarted services
– File access/update times
Covert Channels
• Communication channels that disguises data while it moves
across the network to avoid detection
• Require a client and server
• Can be used to remotely control a machine and to secretly
transfer files or applications
Figure 11.5 A covert channel
between a client and a server
Tunneling
• Carrying one protocol inside another protocol
– Eg. Tunneling AppleTalk traffic over IP
• Any communications protocol can be used to transmit
another protocol
– SSH protocol used to carry telnet, FTP, or X-Windows session
• Used by covert channels
– Loki
– Reverse WWW Shell
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