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CS 6823 –Network Security
Lab 1 Overview
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Task 1: SYN Flood Attacks
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Test telnet during a SYN Flood, with SYN Flood protections ON and OFF
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There are two SYN Flood protection methods:
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SYN Cookies
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Reserve TCP Connections for “proven destinations”
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Task 2: TCP RST Attack
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Guess the correct SEQ/ACK Number to perform a RST Attack
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5% bonus for fully automating the attack
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Task 3: TCP Session Hijacking
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Guess the correct SEQ/ACK, 5% for automating the attack
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Task 4:
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Reverse shell. Same as Task 3, but add a reverse shell exploit
SYN flood defense: SYN cookies (1)
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When SYN segment arrives, host B calculates function (hash) based on:
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Apache example: Source and destination IP addresses and port numbers, and a secret number
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Host B uses resulting “cookie” for its initial seq # (ISN) in SYNACK
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Host B does not allocate anything to half-open connection:
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Does not remember A’s ISN
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Does not remember cookie
SYN flood defense: SYN cookies (2)
If SYN is legitimate
Host A returns ACK
Host B computes same function, verifies function = ACK # in ACK segment
Host B creates socket for connection
Legit connection established without the need for half-open connections
If SYN-flood attack with spoofed IP address
No ACK comes back to B for connection.
No problem: B is not waiting for an ACK
TCP RST Attack
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Attacker can break the TCP connection by sending a TCP RST
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Must match the SEQ and ACK Numbers
Session hijacking
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Take control of one side of a TCP connection
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Marriage of sniffing and spoofing
Session hijacking: The details
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Attacker is on segment where traffic passes from Alice to Bob
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Attacker sniffs packets
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Sees TCP packets between Bob and Alice and their sequence numbers
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Attacker jumps in, sending TCP packets to Bob; source IP address = Alice’s IP address
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Bob now obeys commands sent by attacker, thinking they were sent by Alice
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Principal defense: encryption w/ auth protocol
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Attacker does not have keys to encrypt and insert meaningful traffic