This step by step guide shows what you can do if an abnormal TCP flag attack is detect.
Introduction
An "Abnormal TCP flag attack detected" message from a firewall indicates that the firewall has detected a potentially malicious network traffic pattern involving TCP (Transmission Control Protocol) flags. TCP flags are control bits within the TCP header used to manage the connection between two devices during data transmission. They control actions such as establishing a connection, acknowledging received data, and terminating the connection.
A TCP flag attack involves manipulating these control bits in a way that is abnormal or unintended, aiming to exploit vulnerabilities in the TCP protocol or the devices involved in the communication. This type of attack can be used to bypass security measures, gain unauthorized access, disrupt communication, or perform other nefarious actions.
Remember, prevention is key, and a multi-layered security approach is crucial for protecting networks from various cyber threats, including abnormal TCP flag attacks.
TCP Flag Attacks Detected in Firewall
This issue occurs when the device receives packets with:
(1) ALL TCP flags bit are set at same time.
(2) SYN, FIN bits are set at same time.
(3) SYN, RST bits are set at same time.
(4) FIN, RST bits are set at same time. (usually occurs on the Mac OS)
(5) Only FIN bit is set.
(6) Only PSH bit is set.
(7) Only URG bit is set.
Therefore, the device detects and regards these packets as attacks.
If you are sure these packets are safe, you can log into the device and enter the following CLI commands to disable this detection:
Router(config)# secure-policy abnormal_tcp_flag_detect deactivate
Older models (usg100,200) firmware 3.30 Version =
Router(config)# firewall abnormal_tcp_flag_detect deactivate
If you're not sure if these packets are safe you can try to prevent these packets by focusing on prevention and mitigation rather than an immediate removal, as the attack is typically a symptom of a larger security issue. Firewall and network administrators should implement security measures to protect against such attacks. Regularly updating firewall rules, configuring proper access controls, and using intrusion detection and prevention systems (IPS) can help safeguard the network from TCP flag attacks.