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Linux Kernel sysctl Hardening

Table of Contents

Overview

This is a combined list of all the sysctl hardening recommendations I could find across multiple sites:

Documentation

Documentation for most of these keys can be found at https://github.com/torvalds/linux/blob/master/Documentation. However, the documentation seems to be for the 2.2 kernel. I cannot find any newer documentation. If you know where I can find newer documentation please submit a new issue.

Disclaimer

I do not know what most of these settings do. This list is being provided just as reference material. I take no responsibility for anything.

Keys

key=value Note [Documentation
fs.file-max = 65535 /sysctl/fs.txt
fs.protected_hardlinks = 1 /sysctl/fs.txt
fs.protected_symlinks = 1 /sysctl/fs.txt
fs.suid_dumpable = 0 /sysctl/fs.txt
kernel.core_uses_pid = 1 /sysctl/kernel.txt
kernel.ctrl-alt-del = 0 /sysctl/kernel.txt
kernel.kptr_restrict = 2 /sysctl/kernel.txt
kernel.maps_protect = 1
kernel.msgmax = 65535 /sysctl/kernel.txt
kernel.msgmnb = 65535 /sysctl/kernel.txt
kernel.pid_max = 65535 /sysctl/kernel.txt
kernel.randomize_va_space = 2 /sysctl/kernel.txt
kernel.shmall = 268435456 /sysctl/kernel.txt
kernel.shmmax = 268435456 /sysctl/kernel.txt
kernel.sysrq = 0 /sysctl/kernel.txt
net.core.default_qdisc = fq /sysctl/net.txt
net.core.dev_weight = 64 /sysctl/net.txt
net.core.netdev_max_backlog = 16384 /sysctl/net.txt
net.core.optmem_max = 65535 /sysctl/net.txt
net.core.rmem_default = 262144 /sysctl/net.txt
net.core.rmem_max = 16777216 /sysctl/net.txt
net.core.somaxconn = 32768 /networking/ip-sysctl.txt
net.core.wmem_default = 262144 /networking/ip-sysctl.txt
net.core.wmem_max = 16777216 /networking/ip-sysctl.txt
net.ipv4.conf.all.accept_redirects = 0 /networking/ip-sysctl.txt
net.ipv4.conf.all.accept_source_route = 0 /networking/ip-sysctl.txt
net.ipv4.conf.all.bootp_relay = 0 /networking/ip-sysctl.txt
net.ipv4.conf.all.forwarding = 0 /networking/ip-sysctl.txt
net.ipv4.conf.all.log_martians = 1 /networking/ip-sysctl.txt
net.ipv4.conf.all.proxy_arp = 0 /networking/ip-sysctl.txt
net.ipv4.conf.all.rp_filter = 1 /networking/ip-sysctl.txt
net.ipv4.conf.all.secure_redirects = 0 /networking/ip-sysctl.txt
net.ipv4.conf.all.send_redirects = 0 /networking/ip-sysctl.txt
net.ipv4.conf.default.accept_redirects = 0 /networking/ip-sysctl.txt
net.ipv4.conf.default.accept_source_route = 0 /networking/ip-sysctl.txt
net.ipv4.conf.default.forwarding = 0 /networking/ip-sysctl.txt
net.ipv4.conf.default.log_martians = 1 /networking/ip-sysctl.txt
net.ipv4.conf.default.rp_filter = 1 /networking/ip-sysctl.txt
net.ipv4.conf.default.secure_redirects = 0 /networking/ip-sysctl.txt
net.ipv4.conf.default.send_redirects = 0 /networking/ip-sysctl.txt
net.ipv4.conf.eth0.accept_redirects = 0 change eth0 to your network interface /networking/ip-sysctl.txt
net.ipv4.conf.eth0.accept_source_route = 0 change eth0 to your network interface /networking/ip-sysctl.txt
net.ipv4.conf.eth0.log_martians = 0 change eth0 to your network interface /networking/ip-sysctl.txt
net.ipv4.conf.eth0.rp_filter = 1 change eth0 to your network interface /networking/ip-sysctl.txt
net.ipv4.conf.lo.accept_redirects = 0 /networking/ip-sysctl.txt
net.ipv4.conf.lo.accept_source_route = 0 /networking/ip-sysctl.txt
net.ipv4.conf.lo.log_martians = 0 /networking/ip-sysctl.txt
net.ipv4.conf.lo.rp_filter = 1 /networking/ip-sysctl.txt
net.ipv4.icmp_echo_ignore_all = 1 /networking/ip-sysctl.txt
net.ipv4.icmp_echo_ignore_broadcasts = 1 /networking/ip-sysctl.txt
net.ipv4.icmp_ignore_bogus_error_responses = 1 /networking/ip-sysctl.txt
net.ipv4.ip_forward = 0 /networking/ip-sysctl.txt
net.ipv4.ip_local_port_range = 2000 65000 /networking/ip-sysctl.txt
net.ipv4.ipfrag_high_thresh = 262144 /networking/ip-sysctl.txt
net.ipv4.ipfrag_low_thresh = 196608 /networking/ip-sysctl.txt
net.ipv4.neigh.default.gc_interval = 30
net.ipv4.neigh.default.gc_thresh1 = 32 /networking/ip-sysctl.txt
net.ipv4.neigh.default.gc_thresh2 = 1024 /networking/ip-sysctl.txt
net.ipv4.neigh.default.gc_thresh3 = 2048 /networking/ip-sysctl.txt
net.ipv4.neigh.default.proxy_qlen = 96
net.ipv4.neigh.default.unres_qlen = 6 /networking/ip-sysctl.txt
net.ipv4.route.flush = 1
net.ipv4.tcp_congestion_control = htcp /networking/ip-sysctl.txt
net.ipv4.tcp_ecn = 1 /networking/ip-sysctl.txt
net.ipv4.tcp_fastopen = 3 /networking/ip-sysctl.txt
net.ipv4.tcp_fin_timeout = 15 /networking/ip-sysctl.txt
net.ipv4.tcp_keepalive_intvl = 15 /networking/ip-sysctl.txt
net.ipv4.tcp_keepalive_probes = 5 /networking/ip-sysctl.txt
net.ipv4.tcp_keepalive_time = 1800 /networking/ip-sysctl.txt
net.ipv4.tcp_max_orphans = 16384 /networking/ip-sysctl.txt
net.ipv4.tcp_max_syn_backlog = 2048 /networking/ip-sysctl.txt
net.ipv4.tcp_max_tw_buckets = 1440000 /networking/ip-sysctl.txt
net.ipv4.tcp_moderate_rcvbuf = 1 /networking/ip-sysctl.txt
net.ipv4.tcp_no_metrics_save = 1 /networking/ip-sysctl.txt
net.ipv4.tcp_orphan_retries = 0 /networking/ip-sysctl.txt
net.ipv4.tcp_reordering = 3 /networking/ip-sysctl.txt
net.ipv4.tcp_retries1 = 3 /networking/ip-sysctl.txt
net.ipv4.tcp_retries2 = 15 /networking/ip-sysctl.txt
net.ipv4.tcp_rfc1337 = 1 /networking/ip-sysctl.txt
net.ipv4.tcp_rmem = 8192 87380 16777216 /networking/ip-sysctl.txt
net.ipv4.tcp_sack = 0 /networking/ip-sysctl.txt
net.ipv4.tcp_slow_start_after_idle = 0 /networking/ip-sysctl.txt
net.ipv4.tcp_syn_retries = 5 /networking/ip-sysctl.txt
net.ipv4.tcp_synack_retries = 2 /networking/ip-sysctl.txt
net.ipv4.tcp_syncookies = 1 /networking/ip-sysctl.txt
net.ipv4.tcp_timestamps = 1 /networking/ip-sysctl.txt
net.ipv4.tcp_tw_recycle = 0
net.ipv4.tcp_tw_reuse = 1 /networking/ip-sysctl.txt
net.ipv4.tcp_window_scaling = 0 /networking/ip-sysctl.txt
net.ipv4.tcp_wmem = 8192 65536 16777216 /networking/ip-sysctl.txt
net.ipv4.udp_rmem_min = 16384 /networking/ip-sysctl.txt
net.ipv4.udp_wmem_min = 16384 /networking/ip-sysctl.txt
net.ipv6.conf.all.accept_ra=0 /networking/ip-sysctl.txt
net.ipv6.conf.all.accept_redirects = 0 /networking/ip-sysctl.txt
net.ipv6.conf.all.accept_source_route = 0 /networking/ip-sysctl.txt
net.ipv6.conf.all.autoconf = 0 /networking/ip-sysctl.txt
net.ipv6.conf.all.forwarding = 0 /networking/ip-sysctl.txt
net.ipv6.conf.default.accept_ra_defrtr = 0 /networking/ip-sysctl.txt
net.ipv6.conf.default.accept_ra_pinfo = 0 /networking/ip-sysctl.txt
net.ipv6.conf.default.accept_ra_rtr_pref = 0 /networking/ip-sysctl.txt
net.ipv6.conf.default.accept_ra=0 /networking/ip-sysctl.txt
net.ipv6.conf.default.accept_redirects = 0 /networking/ip-sysctl.txt
net.ipv6.conf.default.accept_source_route = 0 /networking/ip-sysctl.txt
net.ipv6.conf.default.autoconf = 0 /networking/ip-sysctl.txt
net.ipv6.conf.default.dad_transmits = 0 /networking/ip-sysctl.txt
net.ipv6.conf.default.forwarding = 0 /networking/ip-sysctl.txt
net.ipv6.conf.default.max_addresses = 1 /networking/ip-sysctl.txt
net.ipv6.conf.default.router_solicitations = 0 /networking/ip-sysctl.txt
net.ipv6.conf.eth0.accept_ra=0 change eth0 to your network interface /networking/ip-sysctl.txt
net.ipv6.conf.eth0.autoconf = 0 change eth0 to your network interface /networking/ip-sysctl.txt
net.ipv6.ip6frag_high_thresh = 262144 /networking/ip-sysctl.txt
net.ipv6.ip6frag_low_thresh = 196608 /networking/ip-sysctl.txt
net.ipv6.route.flush = 1
net.unix.max_dgram_qlen = 50 /networking/ip-sysctl.txt
vm.dirty_background_ratio = 5 /sysctl/vm.txt
vm.dirty_ratio = 30 /sysctl/vm.txt
vm.min_free_kbytes = 65535 /sysctl/vm.txt
vm.mmap_min_addr = 4096 /sysctl/vm.txt
vm.overcommit_memory = 0 /sysctl/vm.txt
vm.overcommit_ratio = 50 /sysctl/vm.txt
vm.swappiness = 30 /sysctl/vm.txt
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