Understanding ACK Scan DoS Attacks: Detection and Mitigation

How does an ACK Scan DoS Attack Work?

A Transmission Control Protocol (TCP) handshake method flaw is used by an ACK Scan DoS attack. During a normal TCP handshake, the device that wants to start a connection sends a SYN packet to the device that will be getting it. The receiving device sends back a SYN-ACK packet to say that it got the request and is ready to set up the link. Lastly, the device that made the link sends an ACK packet to confirm the connection and end the handshake.

In an ACK Scan DoS attack, the attacker sends a packet to the target system’s interesting port that has the ACK flag set and a sequence number of 0. This goes against the rules for the sequence number option in TCP. When this packet is sent to the target system, that system sends back a Reset (RST) packet. If the RST packet is there, it means that the host is still living but may be behind a filter, such as a firewall, router, or proxy.

By looking at the answers they get, attackers can figure out what kind of firewall or blocking is in place. When paired with SYN scanning, ACK scanning also helps figure out if a firewall is stateful or not. With these methods, the attacker can find out about the network’s weaknesses and possible attack paths.

Detecting and Mitigating ACK Scan DoS Attacks

To successfully find and stop ACK Scan DoS attacks, it is important to use security best practices and proactive measures. Here are some ideas to think about:

1. Network Traffic Monitoring and Analysis
   Use strong tools for monitoring and analyzing network data to find unusual patterns and suspicious activities. These tools can help find ACK Scan DoS attacks by looking at how packets behave, finding things that aren’t normal, and sending out alerts when appropriate.
2. Intrusion Detection and Prevention Systems (IDPS)
   Install Intrusion Detection and Prevention Systems to actively watch network data and find possible ACK Scan DoS attacks. IDPS systems use signature-based detection algorithms to match known attack trends and behavior-based detection techniques to find unusual things that could be signs of an ongoing attack.
3. Firewall and Router Configuration
   Set up defenses and routers so that ACK Scan DoS attacks can’t get through. Control how many ACK packets can be sent per second by using access control lists (ACLs) and rate-limiting methods. Use traffic blocking methods like deep packet inspection (DPI) to find and get rid of malicious ACK packets that act in strange ways. Consider setting up stateful packet inspection (SPI) to study TCP connection states, allowing only legal connections and dropping malicious ACK packets.
4. Intrusion Prevention Rules
   Set up intrusion protection rules to find patterns of ACK Scan DoS attacks and take the right steps. For instance:

   alert tcp 172.16.16.0/24 any to 172.16.17.0/24 any (flags:A; ack:0; message: "Potential ACK Scan"; sid:10001;) 
   alert tcp 172.16.16.0/24 any -> 172.16.17.0/24 any (flags:AR; message: "ACK and RST Detected - Potential ACK Scan"; sid: 10002)

   These rules look for ACK packets with a sequence value of 0 or a RST packet with the ACK flag set, both of which could be signs of an ACK Scan DoS attack.

5. Implement Strong IP Filtering
   Use IP filtering methods to get rid of packets that come from unknown or suspicious sources. This can be done by setting up a firewall or using certain IPtables instructions. For instance:

   $ sudo iptables --append INPUT --source 123.123.123.123 --jump DROP
   

6. Regular Patching and Updates
   Make sure that all network devices, routers, firewalls, and operating systems have the latest patches and updates for protection. Applying patches on a regular basis helps fix known security holes and improves the general security of a network.

Conclusion

ACK Scan DoS attacks are a serious threat to network infrastructure because they could cause service interruptions and make it harder to access systems. Organizations can make their defenses stronger against ACK Scan DoS attacks by putting in place effective ways to find and stop attacks, such as tracking network traffic, intrusion detection and prevention systems, firewall and router configurations, and strong IP filtering. Patching and updating network equipment on a regular basis is also a key part of keeping a network safe. Stay aware and take action to keep your network safe from online threats that are always changing.