JMU GenCyber Boot Camp Summer, 2015

Network Sniffing Sometimes it is possible observe/record traffic traveling on a network Network traffic may contain valuable information: –Usernames and passwords Encrypted Unencrypted – , web requests (and replies), data files –Etc. A sniffer is a piece of software that captures network traffic

Analogy - Wiretapping The FBI conducts wiretaps –Go to a judge and get a court order authorizing the wiretap Who? What? When? Why? –With the help of the phone company, can listen to/record a suspect’s phone conversations to obtain evidence

Analogy – Wiretapping (cont) Sniffer allows an administrator (or attacker) to record/listen in on conversations between computers –May need authorization to monitor network traffic –Electronic Communications Privacy Act – –May not need authorization to monitor network traffic –“Trap and Trace”/”Pen register” –Consent –May not care - attackers

Sniffing - Environment Some networks use shared media so passive sniffing is very easy –Network interface cards can be placed in “promiscuous” mode so that they do not ignore traffic to other hosts Wireless network traffic can also be captured (but may be encrypted) Sniffing is more difficult (but not impossible) in switched environments

Protocol Analysis Captured network packets contain binary data which is difficult to interpret Most sniffers include a protocol analysis component which organizes and displays the (human-readable) contents of the traffic –Example: Wireshark

Example – An Nmap Port Scan Target host: –Start Wireshark Source host: –Perform a TCP-connect scan nmap –sT View results

Example – A Web Connection Target host: –Start Wireshark Source host: –Open a text-based web browser Get default web page on the target host View results

Example – An FTP Connection Target host: –Start Wireshark Source host: –Use the ftp client ftp View results

Example – An SFTP Connection Target host Source host –Use the sftp client sftp View results

Man-in-the-Middle In a switched environment a host only receives: –Traffic destine for itself –Broadcast traffic Cannot see traffic between other hosts Man-in-the-middle = insert yourself as an (undetected) intermediary between communicating hosts

Man-in-the-middle (cont) Normal: Man-in-the-middle: AliceBobIAliceBobI

Man-in-the-middle (cont) How to achieve man-in-the-middle in a switched environment? Exploit address resolution protocols

Address Resolution All network communications must be carried out over physical networks –Each machine has a unique physical address Programs (and humans) use IP addresses to specify the machine to which a message is sent The address resolution problem – need to map IP address to physical address

The Address Resolution Problem Hosts A and B are on the same physical network B wants to communicate with A but only knows A’s IP address EDCBA

The Address Resolution Protocol (ARP) Host A wants to resolve the IP address I B Host A broadcasts a special (ARP) packet that asks the host with IP address I B to respond with its physical address All hosts receive the request Host B recognizes its IP address Host B sends a reply containing its physical address

ARP Phase 1: Phase 2: AXB Y AXB Y

ARP Caches Each host maintains a cache of recently- used mappings –Information in the cache expires after a set time has elapsed When sending an ARP request a host includes its IP-to-physical address binding All machines on a physical network “snoop” ARP packets for mappings

Demo – ARP Cache Host.141 has not communicated with.143 –.141’s ARP cache probably doesn’t contain an entry for.143 Host.141 makes a web request to.143 –ARP for.143’s physical address Added to.141’s cache –Web request sent and reply received

ARP Cache Poisoning Broadcast ARP replies associating your physical address with a given IP address –Other hosts receive this message and put the mapping into their ARP cache –When a machine wants to communicate with the given IP address it sends the frame to your physical address –You read the frame and then forward it on to the real destination host

Cain and Abel A man-in-the-middle LAN attack tool –Sniffer –Protocol analyzer URL: Can be used to poison hosts ARP caches

Demo – ARP Cache Poisoning Hosts.142 and.143 may or may not have communicated –ARP caches may or may not contain entries for each other Start Cain (on.141) and poison both.142 and.143’s ARP caches: –.142’s HW address associated with.141’s IP –.143’s HW address associated with.141’s IP

ARP Cache Poisoning - Result.142 and.143 will communicate with each other –May not realize that their communications are flowing through a third-party All communications will flow through.141 –.141 can read/store traffic –.141 forwards between the two hosts

Example – An FTP Connection Switched Environment –Source host:.143 –Destination host:.142 –Attacker:.141 Using: –Cain and Abel

ARP Poisoning Can: Read traffic Modify traffic

Example – DNS Spoofing Switched Environment –Source host:.143 –Destination host: Google –Attacker:.141 Using: –Cain and Abel

Example – SSH Downgrade Switched Environment –Source host: my laptop –Destination host:.147 –Attacker:.141 Using: –Cain and Abel

ARP Poisoning What attackers look for: –Sensitive, unencrypted communications Web requests/replies, , FTP –Weakly-encrypted communications Old versions of SSH, RDC

ARP Poisoning - Countermeasures Static ARP tables/smart switch ARPwatch IDS

Summary Network traffic may contain valuable information: –Usernames and passwords Encrypted Unencrypted – , web requests (and replies), data files –Etc. ARP poisoning can allow an attacker to capture and modify network traffic as a man-in-the-middle: –Cain and Abel