Ensure TCP SYN Cookies is enabled

보통레벨 1자동cos

설명

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 verify that it has received a valid response to a SYN cookie and allow the connection, even though there is no corresponding SYN in the queue. Attackers use SYN flood attacks to perform a denial of service attacked on a system by sending many SYN packets without completing the three way handshake. Thi...

점검 방법

감사 방식: 셸 명령

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

예상 출력: compliant

조치 방법

조치 방식: 가이드 또는 인프라 패치

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 /etc is stateless on Container-Optimized OS. Therefore, /etc cannot be used to make these changes persistent across reboots. The steps mentioned above needs to be performed after every boot.

속성

운영 체제: 모두
태그: container-optimized-oscos
참고 자료: CIS Google Container-Optimized OS Benchmark v1.2.0 - 3.2.8 Ensure TCP SYN Cookies is enabled

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