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 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.

DNS Monitoring explained

DNS Monitoring gives you the ability to manage and examine the performance of a DNS server. The main goal is to assist you with detecting server-side and client-side DNS issues. In addition, it guarantees the health of DNS servers by sending a DNS request. You are able to choose different query types depending on the DNS record you want to check, for example, A, AAAA, MX, NS, PTR, or CNAME. Then you specify a required expected response that is compared to the actually received response.

DNS Monitoring has a very important role in your network Monitoring service. Moreover, it ensures the safety and proper connection between the end-users and the website or service that they want to use. It is extremely useful when it comes to the fast detection of unpleasant issues or for recognizing potential security breaches. Additionally, it is helpful for stopping some popular malicious attacks. Thanks to the regular checks, you can effortlessly detect unexpected issues or localize DNS outages. As a result, you can prevent a large negative impact on your website or on the safety of your users that want to reach your services by detecting and resolving the problem fast.

Why is DNS Monitoring important?

The Domain Name System (DNS) is an essential part of the Internet. Yet, it was not designed with security in mind. For that reason, cybercriminals have developed ways to take advantage of its vulnerabilities. Therefore, DNS monitoring is vital for helping you protect your online presence and catch issues before they become significant problems. DNS monitoring gives you the ability to recognize several different DNS errors. The majority of them result from malicious attempts and could be a significant threat to your security. On the other hand, there are also communication flow interruptions. They compromise the functionality of your domain’s DNS resolution process and lower the traffic toward your site.

Configuration Errors

DNS Monitoring can detect errors like incorrect IP addresses and assure that outages are not prolonged. The less time your website or service is down, the less your traffic flow is interrupted. That way, you can maintain and increase your uptime, and every user that wants to reach your website (or service) will have that opportunity without any difficulties.

A configuration error can stop users from reaching your website and make it seem like their internet is not acting correctly. This could drive traffic away from your domain and meddle with your business.

DNS Spoofing (DNS poisoning)

DNS Spoofing, also commonly known as DNS poisoning, is a popular cyber threat that cybercriminals use. Recursive DNS servers hold the hostname data with all related DNS records for a particular amount of time (depending on the TTL). That way, they operate more efficiently because they do not repeat the resolution process for the same IP address. However, it also leads to vulnerabilities.

Cybercriminals insert fraudulent data into the DNS cache on the server, like fake IP addresses. Commonly, that is achieved due to viruses and malware. As a result, the users’ requests are directed to a malicious phishing website, which looks similar to the original one. There they type their sensitive information, such as passwords, credit card details, etc. A lot of people do not even notice that they have been directed to malicious pages. No one wants to put its clients at risk of phishing schemes. Additionally, compromising user information can seriously impact your business.

DDoS and DoS Attacks

Distributed Denial of Service (DDoS) and Denial of Service (DoS) attacks are massive cyber threats that are able to bring down your server. They involve large amounts of fake traffic with the main goal of overcoming your resources and making your website or service unavailable for regular users. It is important to mention that the earlier the attack is detected, the more quickly it can be handled. Therefore, it is best to stop it before the DNS records on the server become weaponized by the cybercriminals.

DNS Tunneling

DNS Tunneling is another cyber threat that attackers commonly use. Typically, DNS servers handle a massive amount of traffic, and there are no security measures regarding the exchanged data packets. DNS Monitoring can help detect tunneling and serve to prevent any further data from being exchanged. This is an essential addition to your existing security measures.

DNS outage

DNS outage does not allow your users to connect and reach your website or service. It is possible to last just several minutes, but it could continue up to several hours or even days. So you can probably imagine how seriously it can affect your business and services. With DNS Monitoring, you can easily find and understand where the issue is coming from and quickly fix it.

How does it work?

You can find DNS monitoring as a part of ClouDNS Monitoring service. It works by regularly checking if the DNS server responds to all DNS queries. With such type of check, you can initiate DNS queries for a desired hostname and query type – A (for IPv4), AAAA (for IPv6), MX, NS, PTR, or CNAME. There are two scenarios that follow once you set your expected response.

• The check is marked UP, when the received response is equal to the required expected one.
• The check is marked DOWN, when the received response is not equal to the required expected one.

The DNS monitoring check validates the conditions of DNS servers by sending a DNS request and comparing the received response with the expected one.

You can also take a look at our article about DNS monitoring Checks!

Why do you need it?

DNS monitoring is necessary because DNS performance is essential to your network, servers, and applications. Thanks to the DNS servers, your website or service works effectively and efficiently, yet they should be monitored for vulnerabilities. In case you neglect their adequate supervision, you may compromise both the security of your business and your clients.

With the ClouDNS Monitoring service, you can keep an eye on your servers and quickly detect any issues. As you know, timing is crucial, so the fast resolving of the issues is going to guarantee the integrity of your servers. So, as a result, everything should continue operating smoothly.

Benefits of DNS monitoring

DNS monitoring is a critical component of any organization’s network management strategy. By monitoring DNS traffic, organizations can proactively identify and address issues before they escalate. Here are some of the main benefits of the implementation of DNS monitoring:

• Improved Server Availability

It can help improve server availability by identifying and resolving issues that can cause downtime or service disruptions. For example, DNS servers can be vulnerable to hardware or software failures, network connectivity issues, and cyber attacks, which can affect the availability of websites and other online services. DNS monitoring services can detect and alert tech teams of problems before they escalate, allowing them to take proactive measures to resolve them.

• Improved DNS Server Troubleshooting

DNS monitoring can help improve DNS server troubleshooting by providing visibility into the DNS infrastructure and the flow of DNS queries. Tech teams can use DNS monitoring tools to identify blockages, misconfigurations, and other issues affecting the performance of the DNS server. The information helps them troubleshoot and resolve issues more quickly, minimizing downtime and service disruptions.

• Faster Detection of Outages

DNS monitoring can be useful for detecting outages faster by providing real-time visibility into the DNS infrastructure. It can alert tech teams about issues, such as DNS server failures or network connectivity problems, as soon as they occur. That way, IT teams can quickly identify the root cause of the problem and take action to restore services.

Monitoring Plan

Comparison with other monitoring techniques

DNS monitoring is a specialized approach focusing on the health and security of the Domain Name System, which is crucial for translating domain names into IP addresses. While DNS monitoring is vital, it’s one part of a broader network monitoring strategy that includes other techniques such as network performance monitoring, application monitoring, and security information and event management (SIEM). Here’s how DNS monitoring compares with other monitoring techniques:

• Network Performance Monitoring (NPM): NPM tools focus on the performance and availability of networks and network components (like routers and switches). While NPM can identify network congestion and hardware failures that indirectly affect DNS services, DNS monitoring directly assesses DNS health, ensuring that domain name resolution processes are working as expected.
• Application Monitoring: This technique focuses on the performance and availability of specific applications. It can help identify issues within an application that may impact user experience but doesn’t directly monitor DNS processes. DNS monitoring complements application monitoring by ensuring that users can reach the applications in the first place.

Security Information and Event Management (SIEM): SIEM systems collect and analyze aggregated log data from various sources to detect and respond to security incidents. While SIEM can identify security breaches that may indirectly affect DNS services, DNS monitoring provides specific insights into DNS-related security threats, such as DNS spoofing or tunneling attacks.

Conclusion

So, now you know what DNS Monitoring is and why it is so important for your security. First, there are different criminal attempts that could be prevented when you keep an eye on your servers. Additionally, it is beneficial for simplifying the process of finding and fixing network issues. Finally, it helps you prepare and not be surprised in such situations.

The post Monitoring your DNS, should you do it? appeared first on ClouDNS Blog.