NixOS must manage excess capacity, bandwidth, or other redundancy to limit the effects of information flooding types of denial-of-service (DoS) attacks.

DoS is a condition when a resource is not available for legitimate users. When this occurs, the organization either cannot accomplish its mission or must operate at degraded capacity.

Managing excess capacity ensures that sufficient capacity is available to counter flooding attacks. Employing increased capacity and service redundancy may reduce the susceptibility to some DoS attacks. Managing excess capacity may include, for example, establishing selected usage priorities, quotas, or partitioning.

Verify NixOS is configured to use IPv4 TCP syncookies with the following command:

$ sudo sysctl net.ipv4.tcp_syncookies

net.ipv4.tcp_syncookies = 1

If the network parameter "ipv4.tcp_syncookies" is not equal to "1" or nothing is returned, this is a finding.

Configure the audit service to use IPv4 TCP syncookies.

Add the following Nix code to the NixOS Configuration, usually located in /etc/nixos/configuration.nix or /etc/nixos/flake.nix:

boot.kernel.sysctl = { "net.ipv4.tcp_syncookies"=1; };

Rebuild and switch to the new NixOS configuration: $ sudo nixos-rebuild switch