Ensure TCP SYN Cookies is enabled

中レベル 1自動linux

説明

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

チェック方法

監査方法: シェルコマンド

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

期待される出力: compliant

修正方法

修正方法: ガイダンスまたは IaC パッチ

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

プロパティ

オペレーティングシステム: alinux-2
タグ: cis-convertedkernellinuxsysctl
参照: CIS Aliyun Linux 2 Benchmark v1.0.0 ARCHIVE - 3.2.8

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監査が許可されているマシンで実行してください。スキャンは読み取り専用です。

shell

tmaegis scan --target linux