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Learn How to Defend Against SYN Flood Attacks

By Tom Seest

Are You Prepared for a SYN Flood Attack?

At BestCybersecurityNews, we help entrepreneurs, solopreneurs, young learners, and seniors learn more about cybersecurity.

Your data requires protection — from computers and smart devices to routers and networks. Basic cybersecurity techniques like deleting suspicious attachments or not connecting untrusted USB drives remain vital, but with today’s rapidly evolving threat landscape involving fake IP addresses as well, more comprehensive protection may be necessary than ever.
SYN flood attacks take advantage of how TCP three-way handshake works to create many half-open connections on servers, using resources that could otherwise be utilized for legitimate communication and cripple or disrupt business operations. It is a form of DoS attack and should be treated accordingly.

Are You Prepared for a SYN Flood Attack?

Are You Prepared for a SYN Flood Attack?

What makes SYN Flood Attacks so dangerous?

Denial-of-service attacks (DoS) involve attempts to take down networks or servers by flooding them with excessively large volumes of malicious traffic aimed at debilitating them and stopping them from fulfilling legitimate requests. Depending on the type of DoS attack used, attacks could target individual servers or the entire network and result in significant business disruption and revenue loss.
SYN flood attacks are a type of DDoS attack designed to overwhelm TCP connection handshake protocols. By exploiting the three-way handshake required to establish TCP/IP connections between client and server, this attack floods their open ports with large volumes of SYN packets intended to prevent legitimate connections from being processed and thus deny service to all clients.
SYN floods are typically conducted by an organized collection of computers that have been compromised to serve as zombie bots – collectively referred to as a botnet – which are programmed to send SYN packets on command to their intended targets, making SYN floods one of many Distributed Denial-of-Service (DDoS) attacks.
SYN flood attacks involve malicious clients sending multiple SYN packets using fake or fabricated IP addresses, which are then received by their target server and placed in its SYN queue before waiting for an acknowledgment packet but never receiving one – leading to half-opened connections that drain the system resources.
An aggressive TCP attack can be devastating as the server will be unable to close down the new connections quickly, potentially leading to its crash or becoming unresponsive. To combat such an assault, network administrators can implement SYN cookies so the server won’t accept new connections until its SYN queue has cleared out; they may also tweak TCP stacks so SYN packets arrive sooner and the server accepts them more readily.
SYN floods continue to pose a substantial risk for businesses. Even with mitigation techniques in place, SYN floods can still pose a considerable threat, leading to poor network performance, decreased productivity, loss of revenue, and damaged reputations. For this reason, businesses should employ a multilayered defense against DDoS attacks by training employees on how to identify suspicious activity and using firewalls with DNS filtering capabilities as well as SYN detection devices as safeguards.

What makes SYN Flood Attacks so dangerous?

What makes SYN Flood Attacks so dangerous?

What Makes a SYN Flood Attack So Devastating?

Every day, your computer conducts thousands of conversations with various servers. When initiating these dialogues, a three-part handshake takes place between the client (your computer) and the server to establish their connection: first, the client sends a SYN packet to the server, followed by the server sending SYN-ACK back. Once both parties exchange SYN-ACK packets successfully, a TCP connection will be made.
SYN flood attacks sidestep this step by sending multiple SYN packets to the server without ever sending back an ACK packet, leaving an overcrowded SYN-ACK queue that can’t prevent other requests from coming through.
Denial of service attacks can quickly overwhelm a network, crippling or shutting it down altogether, leaving legitimate users unable to access applications, data, and services that they rely on – for organizations, this could mean lost revenues and business continuity issues while for consumers this could mean they cannot shop online or access social media platforms.
As there is no single solution to protecting against SynN flood attacks, multiple layers of defense must be implemented. This includes installing an intrusion prevention system, maintaining a strong firewall, and using commercial monitoring tools.
Another effective strategy for combatting malicious SYN packets is the implementation of a SYN cookie, which acts as an identification and blocking mechanism. A SYN cookie is a special packet sent from server to client that contains an encrypted sequence number for verifying SYN and ACK packets sent from server, as well as keeping track of their sequence to determine whether further SYN-ACK sessions should continue or terminate altogether.
SYN cookies can be especially effective against SYN flood attacks because they do not depend on a three-way TCP/IP handshake for connectivity establishment. Unfortunately, however, SYN flood attacks remain difficult to mitigate given their attack vector: packets sent via SYN floods may use fake IP addresses that mask their true origin, making it more difficult for security professionals to detect them.

What Makes a SYN Flood Attack So Devastating?

What Makes a SYN Flood Attack So Devastating?

How does the SYN Flood Attack Spoofing Work?

Cyber spoofing may bring to mind images of Mel Brooks or Weird Al Yankovic, but cyber spoofing should not be taken lightly. Cyber spoofing is a form of social engineering which takes advantage of trust relationships between humans and computers to gain unauthorized access, steal data, spread malware or launch attacks against systems or devices. Cyber spoofing attacks may use emails, websites, phone calls or DNS servers.
Email Spoofing attacks occur when an attacker sends emails using an apparent sender address that looks trustworthy to a target recipient, with the intent of obtaining login information, spreading malware through links or attachments or extorting money. Email spoofing is commonly employed in phishing campaigns to steal login credentials, spread malware by clicking malicious links, or extract money through fraudulent schemes.
Website spoofing attacks are when an attacker creates a fake website to look similar to a popular end-user destination, like Facebook. This type of deceptive spoofing can be used by criminals to steal credentials and data, spread malware by clicking malicious links or attachments, or as part of an overall DoS attack campaign.
Caller ID spoofing occurs when an attacker makes it appear as though their call is coming from someone or someplace they trust, such as a bank or customer support for a specific service provider. This technique can be used to gain login access, extract money, or install malware onto the target device.
IP spoofing occurs when an attacker alters the source address of IP packets they send across a network in order to conceal their identity or impersonate another computer system. It is a popular tactic used in DDoS attacks as well as volumetric attack methods like DNS amplification.
Do you ever wonder what cybercriminals might be up to when using free Wi-Fi at a coffee shop? They could potentially intercept communications between you and them by forging media access control (MAC) addresses and performing an ARP attack; this method of intercepting communication can then result in a Man-in-the-Middle (MitM) attack, redirecting funds, stealing data or infecting devices with malware.

How does the SYN Flood Attack Spoofing Work?

How does the SYN Flood Attack Spoofing Work?

Can Your Network Withstand a SYN Flood Attack?

Each day, your computer communicates with various servers it connects to using transmission control protocol/internet protocol (TCP/IP) protocols. These conversations form part of TCP/IP’s communication process: clients request connections by sending out SYN (or Synchronize) packets to servers which then respond with SYN-ACK responses before closing them out using SYN-RST (or Synchronize Reset) responses – something that may or may not happen in an SYN flood attack.
SYN flood is a DDoS attack that uses TCP’s three-step handshake to overwhelm servers and render them unresponsive, potentially impacting users as well as disrupting online services such as e-commerce websites.
SYN flood attacks are fortunately mitigated with several countermeasures available today, as noted in the Cloudflare blog. For example, human-readable SYN packet signatures may provide an effective means of mitigating an attack; human-readable fingerprints of malicious packets allow the detection and analysis of which operating systems they originate from; finally, existing patterns can then be compared against these fingerprints to identify attackers and block them.
Other countermeasures to consider are using an Intrusion Prevention System or firewall, installing updated networking equipment and monitoring network traffic. Furthermore, certain load balancers have the capability to handle TCP SYN/SYN-ACK/ACK handshakes that shed attacks before they impact backend servers.
Security professionals and ethical hackers use SYN flooding as part of a penetration test to expose vulnerabilities within systems or networks, but if left undetected or ignored it can quickly overwhelm a server, blocking legitimate connections from coming through and leading to lost business, disruption to critical infrastructure or loss of access to data.
SYN floods pose a threat to almost all organizations with public-facing websites, and monitoring network traffic for unexpected spikes is the key to protecting yourself against them. Regular log reviews may help identify suspicious activity, while port scanners can identify open ports that should be closed off.

Can Your Network Withstand a SYN Flood Attack?

Can Your Network Withstand a SYN Flood Attack?

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