Ensure TCP SYN Cookies is enabled

MédiaNível 1Automatizadalinux

Descrição

When tcp_syncookies is set, the kernel will handle TCP SYN packets normally until the half-open connection queue is full, at which time, the SYN cookie functionality kicks in. SYN cookies work by not using the SYN queue at all. Instead, the kernel simply replies to the SYN with a SYN|ACK, but will include a specially crafted TCP sequence number that encodes the source and destination IP address and port number and the time the packet was sent. A legitimate connection would send the ACK packet of the three way handshake with the specially crafted sequence number. This allows the system to verif

Como é verificado

Método de auditoria: Comando shell

shell

chk() { p=$1; allowed=" $2 "; case $p in net.ipv6.*) [ -d /proc/sys/net/ipv6 ] || return 0;; esac; v=$(sysctl -n "$p" 2>/dev/null) || { echo "$p: not available"; return 1; }; case "$allowed" in *" $v "*) ;; *) echo "$p is $v (running)"; return 1;; esac; sd=$(readlink -e /lib/systemd/systemd-sysctl || readlink -e /usr/lib/systemd/systemd-sysctl); f=$("$sd" --cat-config 2>/dev/null | grep -Po "^\h*${p//./\.}\h*=\h*\K\H+" | tail -n1); [ -n "$f" ] || { echo "$p is not set in any sysctl configuration file"; return 1; }; case "$allowed" in *" $f "*) ;; *) echo "$p is $f in configuration"; return 1;; esac; }; if chk net.ipv4.tcp_syncookies 1; then echo compliant; fi

Saída esperada: compliant

Como é corrigido

Método de correção: Orientação ou patch de infraestrutura

Set the following parameters in /etc/sysctl.conf or a /etc/sysctl.d/* file: net.ipv4.tcp_syncookies = 1 Run the following commands to set the active kernel parameters: # sysctl -w net.ipv4.tcp_syncookies=1 # sysctl -w net.ipv4.route.flush=1

Propriedades

Sistemas operacionais: alinux-2
Tags: cis-convertedkernellinuxsysctl
Referência: CIS Aliyun Linux 2 Benchmark v1.0.0 ARCHIVE - 3.2.8

Verificar este host

Execute isto em uma máquina que você tenha permissão para auditar. A varredura é somente leitura.

shell

tmaegis scan --target linux