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TMA-ALINUX3-3.3.1.18

Ensure net.ipv4.tcp_syncookies is configured

MittelStufe 1Automatisiertlinux

Beschreibung

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

So wird geprüft

Prüfmethode: Shell-Befehl

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
Erwartete Ausgabe
compliant

So wird behoben

Behebungsmethode: Anleitung oder Infrastruktur-Patch

1. Review all files being used by systemd sysctl and comment out or remove all net.ipv4.tcp_syncookies lines that are not net.ipv4.tcp_syncookies=1. Example script: #!/usr/bin/env bash { l_option="net.ipv4.tcp_syncookies" l_value="1" l_grep="${l_option//./(\\.|\\/)}" a_files=() l_systemdsysctl="$(readlink -e /lib/systemd/systemd-sysctl \ || readlink -e /usr/lib/systemd/systemd-sysctl)" l_ufw_file="$([ -f /etc/default/ufw ] && \ awk -F= '/^\s*IPT_SYSCTL=/ {print $2}' /etc/default/ufw)" [ -f "$(readlink -e "$l_ufw_file")" ] && \ a_files+=("$l_ufw_file"); a_files+=("/etc/sysctl.conf") while IFS= read -r l_fname; do l_file="$(readlink -e "${l_fname//# /}")" [ -n "$l_file" ] && ! grep -Psiq -- '(…

Eigenschaften

Betriebssysteme
alinux-3
Tags
cis-convertedkernellinuxsysctl
Referenz
CIS Alibaba Cloud Linux 3 Benchmark v2.0.0 - 3.3.1.18

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