SYN Flood Mitigation with synsanity

GitHub experienced a significant denial of service attack a year ago, prompting the company to develop new mitigation strategies to ensure high availability for its users. One of the attacks, a SYN flood, exploits the TCP handshake process, inundating servers with SYN requests and potentially overwhelming server resources. Traditional methods like SYN cookies, which defer connection state storage until a valid ACK is received, help mitigate such attacks but have limitations in performance and scalability. GitHub's innovative solution, synsanity, is an iptables module for Linux 3.x that functions similarly to SYN cookies but operates more efficiently by generating SYN cookies outside the standard Linux kernel's LISTEN lock. This approach minimizes impact on normal operations and avoids the need for a custom kernel, allowing GitHub to maintain service integrity during high-volume attacks. Synsanity, which has effectively mitigated numerous attacks, is now open-sourced, reflecting GitHub's commitment to community collaboration and scrutiny for robust security solutions.