TCP SYN Floods stand out as one of the more malicious cyberattacks. By flooding servers with fake connection requests, this form of DDoS attack impedes legitimate traffic while draining system resources.
Attackers use various means to make it hard for infrastructures to interact with real users, leading to lost business, data theft, e-commerce shutdown, IT/OT and IoT too.
What is a SYN flood?
SYN flood is one of the oldest forms of denial-of-service attacks (DDoS), still making waves today on the Internet. By exploiting TCP protocols that control communication between servers and clients, this form of cyber threat overwhelms servers with unprocessed requests that prevents them from servicing real connections and prevents service providers from maintaining reliable connectivity for legitimate connections.
Normal TCP connections begin with clients sending a SYN packet to the server to indicate their desire to establish a connection, followed by receiving an acknowledgement that this packet has been sent and that they intend to initiate a session. When performing a SYN flood attack, however, hackers or attackers spoof their IP addresses or use tools such as zombie hosts that send multiple SYN packets at various times and locations from various IPs, with half-open connections established but no final ACK packet ever arriving; leaving resources being used by real users instead.
Once the backlog of connections grows too large, servers begin running out of resources and may start rejecting all new connections until it can catch up with existing half-open ones. This can have dire repercussions for businesses that rely heavily on TCP connections for essential services like e-commerce, web browsing and email services.
SYN floods can be managed in various ways; various IDS/IPS/firewalls/DDoS protection/load balancers/application servers have features to thwart them, from hardware devices in your data center or cloud-based scrubbing services to hybrid solutions which combine these two approaches.
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How does a SYN flood occur?
Under normal TCP connection circumstances, the three-way handshake process begins when a client sends a SYN (synchronize) packet to the server and they reply with an acknowledgment packet (SYN-ACK), thus creating a connection. But in a SYN flood attack, an outside entity sends multiple SYN packets without sending their final ACK packet and thus flooding servers with half-open connections that consume resources and cause system overload.
SYN attacks can target web servers, email servers, cloud and virtual private server hosts, infrastructure servers (like firewalls routers and load balancers) and even your cellular network. Attacker motives range from simply denial of service attacks to damaging critical infrastructure or stealing sensitive information.
To prevent SYN flooding, your organization should utilize rate limiting, filtering, backlog overflow protection and network segmentation strategies onsite or via managed security services from their cybersecurity provider.
Rate limiting restricts the maximum SYN packets sent to your server at one time, helping prevent its capacity from being reached and making it unable to respond to legitimate requests. Filtering involves configuring rules in network devices to recognize and block SYN packets matching certain patterns or IP addresses known for malicious activity – thereby helping keep malicious traffic away from reaching your servers in the first place.
Backlog overflow protection is another effective strategy for mitigating Syn floods by raising the maximum allowed half-open connections that your server can accommodate at once. By raising this threshold, you can limit bogus connections while freeing up server resources for legitimate incoming requests.
SYN attacks can be difficult to identify and counter. Attackers may use IP addresses that differ from their targets’ actual addresses, making it even harder to track down and block an attack. Distributed attacks from multiple infected computers make identification of source harder – making the attacker’s presence even harder to spot and counteract.
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How is a SYN flood mitigated?
Normal clients who send SYN packets to servers are recorded in a queue until an ACK packet from them arrives; when this occurs, resources are then allocated accordingly. A malicious client, using multiple IP addresses to send many SYN packets at once to one server can overwhelm it with half-open connections that consume resources and interfere with legitimate traffic, creating what is known as a SYN flood attack.
SYN flood attacks can be avoided using various measures, including firewalls and proxies that filter out malicious traffic before it reaches their targets, rate limiting (which allows only certain IP addresses access at certain times of day), rate capping, SYN cookie technology (where servers cache information about each SYN packet as it arrives) as well as rate capping are all methods available to reduce its effects.
SYN attacks can either be direct or distributed. When used directly, an attack uses one device with an identifiable IP address to initiate it. By contrast, distributed attacks involve botnets which send malicious packets over a wide network of devices – these types of attacks are more difficult to neutralise due to more difficulty pinpointing and isolating each malicious device.
An SYN attack’s objective is to overwhelm a target server with so many half-open connections that it cannot support any legitimate users, thus depriving victims from access to services or applications they require. Attackers may employ other techniques, such as spoofing or flooding algorithms, in addition to SYN floods to cause even greater havoc.
SYN attacks have long been a feature of life on the internet and commercial significance. As time went on, hackers evolved their tools and techniques in order to evade detection and cause maximum damage – it is therefore essential for organizations to understand how SYN attacks work so they can defend against them effectively.
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What are the warning signs of a SYN flood?
As part of the three-way handshake when initiating TCP/IP connections with servers, clients send SYN packets. Servers then respond with SYN-ACK packets that acknowledge client requests to establish reliable and secure data transfer between both parties. An attacker can launch a SYN flood attack by sending multiple SYN packets without receiving an acknowledgement from target servers; this causes their resources to remain half open instead of allocating them for legitimate connection requests.
SYN flood attacks can be detected by closely watching SYN queues; an increase in queued connections that do not receive an acknowledgement (ACK) could indicate such an attack. Furthermore, monitoring server responsiveness and availability is vital – any sudden decrease in server response speed coupled with an unusually high error or timeout rate could indicate such an assault.
SYN attacks are an extremely damaging form of Distributed Denial-of-Service (DDoS) attacks that can be launched against any system providing TCP/IP services on the Internet. They can create numerous problems, such as losing business continuity, revenue losses and disruption to critical infrastructure – not to mention damage to one’s company reputation.
Hackers frequently utilize SYN attacks as a method for testing their penetration abilities – known as pen testing or ethical hacking, this practice allows hackers to gain entry to internal systems and identify security flaws that could potentially be exploited by malicious actors.
Network administrators can utilize tools such as netstat, which displays information about networking connections and routing tables, to analyze traffic statistics. These tools can be configured to display metrics such as active TCP openings compared to failed connection attempts or SYN-ACK packets sent but not received; for instance, when monitoring for SYN flood attacks.
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