SYN flood attack: Origin and Basics

In the 1990s, a man named Wietse Venema explained a certain attack method in-depth. On its surface, the concept seems innocuous enough. In a network protocol, namely TCP, a three-way handshake commences communication. Imagine this as a modern chivalry ritual between your computer and the server you want to engage with.

1. You send a SYN (synchronize) packet: “Hi, can we chat?“
2. Server sends back SYN-ACK (acknowledgment): “Sure, let’s talk.“
3. You finish with an ACK: “Cool, let’s get started.“

What SYN flood attack is?

Broadly speaking, a SYN flood attack, also referred to as a TCP/IP-based attack, is a type of Denial of Service (DDoS) attack on a system. It might be compared to an irritating prankster continuously dialing a business phone to keep the line busy and prevent legitimate callers from reaching the establishment. The attacker here sends a flood of SYN requests from either a single or multiple spoofed IP addresses to a server with the malicious intent to halt the server’s functionality to process new incoming service requests. As the server gets trapped in a vicious cycle of responding to these inexistent or half-open connections, it can lead to crashing or becoming unavailable to legitimate users.

How does it work? 

The mechanics of a SYN flood operate in a methodical sequence of steps that exploit the TCP handshake protocol. Let’s break it down for clarity:

Step 1: Identifying the Target

The attacker first picks out the target server. Usually, they’re gunning for a specific service, like a website or an application hosted on that server.

Step 2: Initiating SYN Requests

Here, the attacker commences the mischief by generating a multitude of SYN packets. Each of these SYN packets asks the server, in essence, for permission to establish a connection.

Step 3: Half-Open Connections

Upon receiving a SYN request, the server reciprocates with a SYN-ACK packet and moves the corresponding request to a backlog queue. This places the connection in a “half-open” state, awaiting the client’s final ACK for completion.

Step 4: Server Response

At this juncture, the attacker ghosts the server, never sending the final ACK to complete the handshake. Consequently, the server’s backlog queue starts brimming with incomplete handshakes.

Step 5: Resource Exhaustion

With each half-open connection, the server allocates a chunk of its resources. As these incomplete connections accrue, the server begins to hit its limit on resources.

Step 6: Denial of Service

At this point, the server becomes unable to accept any new connections. Legitimate users trying to connect encounter timeouts or failures, achieving the attacker’s endgame of denying service.

Types of SYN Flood Attacks

SYN flood attacks can take on multiple forms, each with its own level of complexity and associated risks:

1. Direct Attack: In this type of attack, the attacker does not hide their IP address, meaning that all traffic comes from a single source. This makes it relatively easier for network administrators to identify and block the attack by filtering the IP address. However, direct attacks can still overwhelm a server, especially if they come from high-capacity sources.
2. Spoofed Attack: Here, the attacker sends SYN requests using spoofed IP addresses, making it difficult to track the origin of the traffic. The server tries to send SYN-ACK packets to non-existent or unreachable IPs, leaving the connections open and slowly exhausting server resources​. Spoofing adds an extra layer of complexity, making it harder to mitigate, as simply blocking the traffic source won’t solve the problem.
3. Distributed Attack (DDoS): In a distributed SYN flood attack, the attacker uses a botnet – a network of compromised devices – to send SYN requests from various IP addresses. This creates massive amounts of traffic from multiple sources, overwhelming the server and making it extremely difficult to pinpoint and block the attack. This method was infamously used by the Mirai botnet, which leveraged IoT devices to launch one of the largest DDoS attacks in history​.

Ways to mitigate the SYN flood attack

Ah, but there’s hope! Multiple strategies can serve as lifelines in mitigating the fallout from a SYN flood.

SYN cookies

Implementing SYN cookies proves useful in minimizing risk. When deployed, the server doesn’t allocate resources right away for a new SYN request. Rather, it converts the connection into a unique cryptographic cookie. Only when the handshake gets completed does the server expend resources, reducing vulnerability to attacks.

Rate limiting

Another solid tactic involves imposing rate limiting on incoming SYN packets. By setting a strict threshold for the number of allowable new connections per unit of time, the server can effectively nip malicious flood attempts in the bud.

DDoS Protection

Incorporating DDoS protection is an advanced, indispensable strategy. These specialized solutions not only defend against SYN flood attacks but also guard against a broader range of DDoS threats. DDoS protection services usually feature large traffic scrubbing networks that can sift through immense volumes of data, allowing legitimate traffic through while blocking malicious requests.

Anycast DNS

Anycast DNS serves as another invaluable layer of defense. By distributing incoming traffic across multiple data centers (PoPs), it minimizes the load on any single server. This distribution can effectively dilute a SYN flood attack, rendering it far less potent. Anycast DNS is especially beneficial when used in conjunction with DDoS protection services, providing an additional layer of robust, scalable defense.

Robust Load balancers
High-capacity load balancers can significantly improve your system’s capacity to manage an enormous volume of connection requests. In turn, this can enhance your network’s ability to resist SYN flood attacks.

Monitoring services
Real-time Monitoring services track and scrutinize network patterns, activities, and performance, enabling the early detection of potential threats or attacks. These services can monitor server health, network performance, and traffic patterns, thereby identifying and alerting about possible anomalies that might indicate a SYN flood attack.

Firewall rules

Tweaking firewall configurations can also be invaluable. For instance, you can set rules to block incoming requests from a specific IP address if it exceeds a set number of SYN requests within a short timeframe.

Suggested article: Router vs firewall

Consequences of non-protection

• Service disruption: SYN flood attacks can result in service disruption or downtime, as the targeted server becomes overwhelmed and unable to handle legitimate requests.
• Financial loss: Downtime can lead to financial losses for businesses, especially e-commerce websites, online services, and organizations heavily reliant on internet connectivity.
• Reputation damage: Frequent DDoS attacks, including SYN floods, can tarnish a company’s reputation, eroding trust and customer confidence.
• Security overhaul costs: Post-attack, merely patching vulnerabilities won’t suffice. A complete revamp of security protocols becomes vital, often draining both time and financial resources.

Conclusion

In a world increasingly reliant on digital technology, understanding and defending against threats like SYN flood attacks is crucial. While they are a potent threat, solutions such as SYN cookies and robust load balancers offer effective means of mitigation. In essence, maintaining cybersecurity is not just a good idea, but a necessity in today’s digital landscape.

The post Understanding SYN flood attack appeared first on ClouDNS Blog.

What is a flood attack?

A flood attack, often a form of Distributed Denial of Service (DDoS) attack, aims to overwhelm a system with superfluous requests, thus preventing legitimate requests from being fulfilled. The primary objective is to make the target service unavailable, either by consuming all its resources or crashing it altogether. Flood attacks exploit the limitations of a network’s bandwidth, memory, and processing power. By sending an excessive number of requests, they can exhaust these resources rapidly, causing severe disruptions. Attackers often use botnets, a network of compromised devices, to generate the enormous volume of traffic required for such attacks, making it harder to trace and block the sources.

How does it work?

A flood attack works by sending a massive volume of traffic to a targeted server, service, or network. This traffic often appears to be from legitimate users, which makes it challenging to distinguish and filter out. The target system gets overwhelmed by this surge in requests, which eventually leads to its degradation or shutdown. Flood attacks can be executed through various protocols and methods, such as TCP, UDP, ICMP, and HTTP, each exploiting different aspects of the network’s communication process. Advanced flood attacks may use randomization techniques to avoid detection and mitigation efforts, making them more sophisticated and harder to counter.

Why is flood attack dangerous?

• Disruption of service: The most immediate impact is the service disruption. Websites may become unavailable, networks may slow down, and businesses may experience downtime.
• Financial impacts: With downtime comes lost revenue. Especially for businesses that rely heavily on online services, a few minutes of inaccessibility can translate to significant financial losses.
• Damage to reputation: Continuous attacks can tarnish a company’s reputation, causing loss of customer trust and loyalty.
• Resource consumption: An immense amount of resources, both human and technological, need to be diverted to handle the aftermath of such attacks.
• Diversion: Sometimes, attackers use flood attacks as a smokescreen, diverting attention from a more covert breach or intrusion.

How to mitigate it?

• Monitoring: Continuous monitoring of network traffic can help in early detection of unusual traffic spikes, which may indicate a flood attack. Tools like intrusion detection systems (IDS) can be invaluable.
• DDoS Protection: DDoS protection services can help mitigate the effects of a flood attack. These services often use a combination of traffic filtering, rate limiting, and other tactics to ensure only legitimate traffic reaches the target. 
• Secondary DNS: If the primary DNS server becomes overwhelmed due to a flood attack, the secondary DNS server can continue to resolve domain names, ensuring that services remain accessible to legitimate users.
• Firewalls and Routers: Properly configured firewalls and routers can help filter out malicious traffic.
  Router vs firewall
• TTL Analysis: Investigate the TTL values on incoming packets. Abnormal TTLs can indicate potential malicious traffic.
• IP Blocklisting: Identify and block IPs that show malicious activity. This prevents them from accessing your systems further.
  Whitelisting vs Blacklisting

Types of flood attack

DNS Flood Attack

A DNS flood attack specifically targets the Domain Name System (DNS) servers. The DNS is the internet’s phonebook, translating human-friendly URLs (like “example.com“) into IP addresses that computers use to identify each other on the network (like “1.2.3.4”). In a DNS flood attack, attackers send a high volume of DNS lookup requests, usually using fake IP addresses. This causes the DNS servers to try and resolve each request, leading to an overwhelming number of processes. This congestion ensures that genuine requests from real users either get significantly delayed or ignored altogether. If an attacker successfully disrupts a DNS server, it can make a whole swath of websites or online services inaccessible.

SYN Flood Attack

To understand a SYN flood attack, one must first grasp the “three-way handshake” process used to establish a TCP connection. The sequence is SYN, SYN-ACK, and ACK. In a SYN flood attack, the attacker sends a rapid succession of SYN requests but either does not respond to the SYN-ACK replies or sends them from spoofed IP addresses. The target system will keep these connections open, waiting for the final ACK that never comes. This can consume all available slots for new connections, effectively shutting out legitimate users.

HTTP Flood Attack

HTTP flood attacks take advantage of the HTTP protocol that web services operate on. In this attack, a massive number of HTTP requests are sent to an application. Unlike other flood attacks, the traffic sent looks legitimate. The requests can be either valid URL routes or a mixture with invalid ones, making them harder to detect. Because the requests look so much like typical user traffic, they’re particularly difficult to filter out. This method can exhaust server resources and cause legitimate requests to time out or receive delayed responses.

ICMP (Ping) Flood Attack

ICMP, or Internet Control Message Protocol, is a network protocol used by network devices to send error messages. The “ping” tool uses ICMP to test the availability of network hosts. In a Ping flood attack, attackers inundate the target with ICMP Echo Request (or ‘ping’) packets. The target then tries to respond to each of these requests with an Echo Reply. If the attack is voluminous enough, the target system’s bandwidth or processing capabilities may get overwhelmed, causing a denial of service.

Suggeted page: The function of ICMP Ping monitoring

UDP Flood

User Datagram Protocol (UDP) is a sessionless networking protocol. In a UDP flood attack, the attacker sends many UDP packets, often with spoofed sender information, to random ports on a victim’s system. The victim’s system will try to find the application associated with these packets but will not find any. As a result, the system will often reply with an ICMP ‘Destination Unreachable’ packet. This process can saturate the system’s resources and bandwidth, preventing it from processing legitimate requests.

Impact of Flood attacks on different industries

Flood attacks can have devastating effects across various industries, each facing unique challenges and potential damages:

E-commerce:

E-commerce platforms rely heavily on their websites for sales and customer interaction. A flood attack can cause significant downtime, leading to lost sales, decreased customer trust, and potential long-term damage to the brand’s reputation. Additionally, the costs associated with mitigating the attack and enhancing security measures can be substantial.

Suggest: Global Reach, Local Touch: The Role of GeoDNS in eCommerce Expansion

Finance:

In the finance sector, the availability and integrity of online services are critical. Flood attacks can disrupt online banking, trading platforms, and payment processing systems. This not only affects customer transactions but can also lead to compliance issues and regulatory scrutiny. The financial losses and impact on customer confidence can be severe.

Healthcare:

Healthcare providers use online systems for patient management, medical records, and telemedicine. A flood attack can interrupt these services, potentially putting patient health at risk. Delayed access to medical records and appointment scheduling can cause significant operational disruptions and affect the quality of care provided.

Gaming:

The gaming industry is a frequent target of flood attacks, especially during major events or game launches. These attacks can disrupt gameplay, causing frustration among users and leading to a loss of revenue for gaming companies. The competitive nature of online gaming also means that downtime can significantly impact player engagement and retention.

Conclusion

Flood attacks are among the oldest tools in a hacker’s arsenal, but they remain effective. As the digital landscape grows and evolves, so do the methods attackers employ. Regularly updating security infrastructure, staying informed about emerging threats, and employing a proactive defense strategy can go a long way in keeping systems secure and operational.

The post Flood Attack: Prevention and Protection appeared first on ClouDNS Blog.

What is a R.U.D.Y. attack?

R.U.D.Y., short for “R U Dead Yet,” is a slow-rate DoS attack that targets web servers and applications. Unlike traditional DoS attacks that overwhelm servers with rapid, high-volume requests, a R.U.D.Y. attack employs a stealthier approach. This attack targets the application layer (Layer 7) of the OSI model, specifically exploiting HTTP POST requests to cause disruption. It works by sending HTTP POST requests with an abnormally long content-length header value, transmitting the data in exceedingly slow chunks. This tactic keeps the server connection open for extended periods, eventually exhausting server resources and causing legitimate user requests to be delayed or denied.

How does it work?

To understand the mechanics of a R.U.D.Y. attack, let’s break it down step-by-step:

1. Initiation: The attacker identifies a target web server that accepts HTTP POST requests.
2. Connection Establishment: The attacker establishes a connection to the server.
3. Sending Headers: The attacker sends an HTTP POST request with an exaggerated content-length header, indicating that a large amount of data will follow. Here is an example:
   POST /submit HTTP/1.1
   Host: targetserver.com
   Content-Length: 100000
4. Slow Data Transmission: Instead of sending the data all at once, the attacker sends the data in very small chunks, with long intervals between each chunk. This slow data transfer ties up server resources. The attacker ensures that each chunk is sent within the timeout limit set by the server, preventing the connection from being dropped.
5. Resource Exhaustion: As more connections are opened and held, the server’s resources are gradually consumed, leading to performance degradation and potential denial of service to legitimate users.

Technical Details

• HTTP POST Request: This method is used to send data to the server, typically for form submissions. The R.U.D.Y. attack exploits this by sending data extremely slowly, maintaining the connection just below the server’s timeout threshold.
• Connection Timeout: Web servers have a timeout setting to drop idle connections. The R U Dead Yet attack aims to stay just within this timeout window, keeping the connection alive indefinitely.
• Application Layer Attack: As a Layer 7 attack, R.U.D.Y. specifically targets the application layer, making it more challenging to detect and mitigate compared to lower-layer attacks like SYN floods or ICMP attacks.

Why is the R U Dead Yet attack effective?

The effectiveness of the R.U.D.Y. attack lies in its simplicity and the difficulty of detection. Traditional DoS defenses, which focus on high traffic volumes and rapid request rates, may not recognize the slow and steady nature of a R.U.D.Y. attack. Additionally, since the attack mimics legitimate user behavior by sending properly formatted HTTP requests, it can bypass many security measures.

Suggested article: HTTP vs HTTPS – All you need to know!

The impact of a R.U.D.Y. attack

The impact of a R U Dead Yet attack can be severe, especially for web servers and applications that rely heavily on maintaining numerous concurrent connections. Some of the consequences include:

• Server Overload: As server resources are consumed by the slow connections, legitimate users experience delays or are unable to connect.
• Increased Latency: The server’s response times become significantly slower, degrading the user experience.
• Potential Downtime: In extreme cases, the server may become completely unresponsive, leading to downtime and potential revenue loss for businesses.
• Resource Depletion: The server’s CPU, memory, and network bandwidth can be exhausted, impacting overall performance and availability.

Defending against R.U.D.Y. attacks

Preventing and mitigating R.U.D.Y. attacks require a multi-faceted approach. Here are some strategies to consider:

1. DDoS Protection Services – Utilizing services that provide distributed denial-of-service (DDoS) protection can help absorb and mitigate the effects of such attacks. ClouDNS DDoS Protection service uses advanced filtering techniques to ensure that malicious traffic is effectively removed before reaching the target server, maintaining the integrity and performance of your online services.
2. Timeout Configuration: Configure server timeouts to limit the duration a connection can remain open without transmitting data. This can help close slow connections before they consume excessive resources.
3. Rate Limiting: Implement rate limiting to control the number of requests a single IP address can make in a given timeframe. This can help identify and block malicious users.
4. Behavioral Analysis: Use security tools that analyze traffic patterns and detect anomalies indicative of slow-rate attacks. Solutions like Web Application Firewalls (WAFs) can be configured to recognize and block suspicious activity.
5. Connection Throttling: Throttle connections based on the rate of data transmission. If data is being sent too slowly, the connection can be terminated.
6. Load Balancing: Distribute traffic across multiple servers to ensure no single server becomes a bottleneck. Load balancers can also help detect and mitigate attack patterns.
7. Regular Monitoring: Implement Monitoring service that will check server performance and traffic for signs of abnormal behavior. Early detection is crucial for mitigating the impact of an attack.

Conclusion

The R.U.D.Y. attack is a sophisticated and stealthy threat that highlights the need for robust and adaptive security measures in today’s digital landscape. By understanding the mechanics of this attack and implementing effective defenses, organizations can better protect their web servers and ensure the availability and performance of their online services. Stay vigilant, keep your defenses up-to-date, and be prepared to counter the evolving tactics of cyber adversaries.

The post R.U.D.Y. (R U Dead Yet) Attack Explained appeared first on ClouDNS Blog.