Disclaimer: This post is strictly for educational purposes. Unauthorized hacking, cracking, or tampering with network systems is illegal and goes against ethical standards. Always seek written consent before performing any security evaluation or examination.
Layer 4 of the OSI model is the Transport layer, which includes TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) that are associated with end-to-end communication in transfer of data. The primary function of the layer is to manage the flow control and error correction of data packets between applications. However, this part of the model faces its fair share of problems, as it is a treasure chest for attackers who want to manipulate, intercept or disrupt data flows. In this paper, we hope to understand the more obscure aspects of Layer 4 hacking and examine how attackers wreak havoc and gain control over this layer.
Exploitation of Transport Layer Techniques:
SYN Flooding:
Technique: One form of denial of service (DoS) attack in which a perpetrator sends a burst of SYN requests to a server to establish TCP connections and does not follow through, which uses all the connections the server is able to establish.
Execution: An attacker can use hping3 or LOIC to target a server with SYN packets, which uses up memory and CPU resources indiscriminately, leaving numerous half-open connections in its wake until all possible connections have been used.
Example: With SYN flood, a typical consequence might be that a server fails to respond to any further connections, thereby denying legitimate users access to the server.
TCP Session Hijacking:
Technique: Taking control of a TCP session either by anticipating the sequence numbers or capturing them.
Execution: To capture and guess sequence numbers, the attacker can use packet capture tools like ettercap which would allow him to place himself in the middle of a session. The attacker subsequently assumes the identity of one end of the session.
Example: An attacker could easily gain access to this system by altering or extracting data by hijacking an admin session.
UDP Flood:
Technique: An attack similar to SYN flooding but for UDP, where the targeted machine is bombarded with UDP packets, overwhelming the machine or network that is processing the packets.
Execution: An attacker can abuse services like echo and chargen to send massive amounts of UDP packets to an unsuspecting target. Systems that are not hardened to handle such stress would end up crashing, and all available bandwidth would be drained in the process.
Example: All available bandwidth is wasted on nonsensical UDP traffic, leaving the network useless.
Port Scanning:
Technique: Scanning for open TCP ports on a target, consequently revealing services that could be exploited.
Execution: Nmap and other tools can carry out different port scanning techniques (SYN, FIN, Christmas, etc) and in doing so, probes the network for intrusion possibilities.
Example: An intruder could try to force brute a captured SSH port or try to use some other known vulnerabilities.
TCP Reset Attacks:
Technique: Closing specific communication sessions by sending false RST packets, thus disrupting communication.
Execution: Observing the network traffic can give practically useful information for sending RST packets and thus terminating the session well before it is required to be terminated. The sequence number is usually guessed or captured host.
Example: Abusing this can cause disruption in online transactions or cause the user not to be able to access their account due to the user being successfully disconnected over and over again.
Visual Strategies: Assimilate Anti-DDoS
- SYN Cookies: Use SYN cookies to avoid resource allocation for half open connections.
- Rate Limiting: Rate limiting can be applied to TCP handshake attempts to reduce possible SYN flood attacks. Restrict the number of connection requests within a given time frame.
- Stateful Firewalls: Place firewalls that filter internet traffic based on permissions granted to previously established connections or the state of the firewalls system.
- Secure Sequence Numbers: Make sure that TCP sequence numbers are random and do not follow any particular pattern to avoid possible hijacking.
- UDP Filtering: Attack surfaces can also be reduced by filtering or limiting traffic from network devices to known vulnerable services.
- Port Hardening: Firewall behavior can be modified by closing unused ports and changing user services to low or no privileges.
The Ethical Hacker’s Responsibility:
- Penetration Testing: Evaluate the level of resistance of the systems to transport layer breaches.
- Vulnerability Assessment: Probe for exposed ports and services for potential disabling or fortification.
- Education: Instruct the network teams on the dangers of Layer 4 attacks and the necessity of strict connection management policies.
Conclusion:
As seen, Layer 4 hacking illustrates how disruptive manipulation of fundamental network protocols can result in dire consequences. Familiarization with these attack methods not only enhances the ability to defend them but also shows how intricate network security is. The Transport layer is a basic standard for reliable data communication and serves as a reminder that every layer of the network stack has to be guarded against with proactive vigilance and planning.
Note: The purpose of this post is to shed light on the means to which attackers can compromise the Transport layer to protect against it.