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Chapter 6

Chapter 6. Gathering Data from Networks: Sniffers. Sniffing Defined. Using a program or device to monitor data traveling through a network Good use: Network management & monitoring Bad use: Steal passwords, email, files. TCP/IP Model. 4 layer model Application Transport Internet

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Chapter 6

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  1. Chapter 6 Gathering Data from Networks: Sniffers

  2. Sniffing Defined • Using a program or device to monitor data traveling through a network • Good use: Network management & monitoring • Bad use: Steal passwords, email, files

  3. TCP/IP Model • 4 layer model • Application • Transport • Internet • Network Access

  4. TCP Header Components • Source Port Urgent Pointer • Destination Port Options • Sequence Number • Ack Number • Data Offset • Reserved • Control Bits • URG, ACK, PSH, RST, SYN, FIN • Window • Checksum

  5. How Sniffers Work • Promiscuous Mode • Capture packets headed for target’s MAC • Most commonly sniffed (unencrypted) • HTTP, POP3, IMAP, SNMP, FTP, Telnet, NNTP • Passive versus Active • Passive needs • Hub (called: shared Ethernet) • Wireless AP • Port mirroring on switch (called: switched Ethernet) • Example: use Trojan to install Back Orifice on target machine. Attacker gets email from “Butt Trumpet” plug-in after installation. Now packet sniffer can be installed.

  6. How Sniffers Work • Passive versus Active • Active needs • ARP spoofing: spoof the gateway’s MAC address • MAC flooding/Traffic-flooding attack: flood switch with fake MAC addresses to overcome the limited memory; causes “failopen mode” • MAC duplicating

  7. Detection & Countermeasures • Hard to detect since no trace is left • Look for machines in promiscuous mode • Run ‘arpwatch’ for changed MAC addresses • Use ‘HP OpenView’ or ‘IBM Tivoli’ for strange packets • Best: encryption • AES • RC4 • RC5

  8. Overcoming Switch limitations • ARP poisoning • Uses ARP spoofing to redirect packets • Result: DoSand MITM • Countermeasures • Static ARP entries in cache

  9. Sniffing Tools • Wireshark: aka Ethereal • open source protocol analyzer; capture traffic in real time • Snort: also packet logger • IDS: detects threats, such as buffer overflows, stealth port scans, CGI attacks, SMB probes and NetBIOS queries, NMAP and other port scanners, well-known backdoors and system vulnerabilities, and DDoS clients, and alerts the user about them. It develops a new signature to find vulnerabilities. • Snortsnarf: converts data collected from Snort into Web pages for easier reading • Sandhain • open source multi-platform application that is used for checking the integrity of centralized files & detecting host-based intrusion (HIDS)

  10. MAC Flooding & DNS Spoofing • Overcoming switched networks • ARP spoofing • sniff data frames on a LAN or stop the traffic altogether • Overwhelm a switch (macof) • DNS Spoofing / Poisoning • Feed the DNS server with incorrect information • Intranet Spoofing • Internet Spoofing • Proxy Server DNS Poisoning • DNS Cache Poisoning • Kaminsky DNS Vulnerability – Summer 2008 • http://unixwiz.net/techtips/iguide-kaminsky-dns-vuln.html

  11. Tools • Wireshark • Dsniff: collection of tools • Filesnarf, mailsnarf, urlsnarf, msgsnarf (Instant Messages) webspy, arpspoof, dnsspoof, macof • Dnspoof • Forges replies to DNS queries • Alerts of spoofed packets • Cain & Abel • MITM attacks; sniffing; ARP poisoning • EtherPeek • Ethercap

  12. Tools • SMAC • Hunt • TCPDump: command-line tool • Network Probe • Snort

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