KULIAH IIITHREAT AND ATTACK (2)

Aswin Suharsono

KOM 15008Keamanan Jaringan

2012/2013

KOM 15008Keamanan Jaringan

2012/2013

Overview

• Phase 3: Gaining Access Using Network Attacks– 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

• 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

Introduction

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

A

B

C

src:B dest:A payload

wireshark software used for end-of-chapter labs is a (free) packet-sniffer

1-6

Introduction

Bad guys can use fake addresses

IP spoofing: send packet with false source address

A

B

C

src:B dest:A payload

1-7

… lots more on security (throughout, Chapter 8)

• 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-of-service 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

• 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

Introduction

target

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

Bad guys: attack server, network infrastructure

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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