Linux-Setup-Scripts/etc/sysctl.d/99-server.conf

# https://madaidans-insecurities.github.io/guides/linux-hardening.html#sysctl
dev.tty.ldisc_autoload = 0

# https://access.redhat.com/solutions/1985633
# Seems dangerous
fs.binfmt_misc.status = 0

# https://madaidans-insecurities.github.io/guides/linux-hardening.html#sysctl-userspace
# Enable fs.protected sysctls
fs.protected_regular = 2
fs.protected_fifos = 2
fs.protected_symlinks = 1
fs.protected_hardlinks = 1

# https://madaidans-insecurities.github.io/guides/linux-hardening.html#core-dumps
# Disable coredumps
# For additional safety, disable coredumps using ulimit and systemd too.
kernel.core_pattern=|/bin/false
fs.suid_dumpable = 0

# Restrict dmesg to CAP_SYS_LOG
# https://www.kernel.org/doc/Documentation/sysctl/kernel.txt
kernel.dmesg_restrict = 1

# https://www.kernel.org/doc/Documentation/sysctl/kernel.txt
# https://madaidans-insecurities.github.io/guides/linux-hardening.html#sysctl-kernel
# https://kernsec.org/wiki/index.php/Bug_Classes/Kernel_pointer_leak
# Restrict access to /proc
kernel.kptr_restrict = 2

# Not needed, I don't do livepatching and reboot regularly.
# On Ubuntu LTS just sed this to be 0 if you use livepatch.
kernel.kexec_load_disabled = 1

# https://madaidans-insecurities.github.io/guides/linux-hardening.html#sysctl
# Basically, restrict eBPF to CAP_BPF.
kernel.unprivileged_bpf_disabled = 1
net.core.bpf_jit_harden = 2

# Docker running as root do not require unpriv user ns, which is dangerous, so we disabe it
kernel.unprivileged_userns_clone = 0

# Needed for gVisor, which is used on almost all of my servers
kernel.yama.ptrace_scope = 1

# https://madaidans-insecurities.github.io/guides/linux-hardening.html#sysctl
# Restrict performance events from unprivileged users as much as possible.
# We are using 4 here, since Ubuntu supports such a level.
# Official Linux kernel documentation only says >= so it probably will work.
kernel.perf_event_paranoid = 4

# https://github.com/containerd/containerd/issues/9048
# Disable io_uring, a very sus feature.
# Note that this will make using Proxmox extremely annoying though, so you might wanna comment this out
# on a Proxmox node.
kernel_io_uring_disable = 2

# https://madaidans-insecurities.github.io/guides/linux-hardening.html#sysctl-kernel
# Disable sysrq
kernel.sysrq = 0

# https://www.stigviewer.com/stig/red_hat_enterprise_linux_6/2020-09-03/finding/V-217911
# Not running a router here, so no redirects
net.ipv4.conf.*.send_redirects = 0
net.ipv4.conf.*.accept_redirects = 0
net.ipv6.conf.*.accept_redirects = 0

# Check if the source of the IP address is reachable through the same interface it came in
# Basic IP spoofing mitigation
net.ipv4.conf.*.rp_filter = 1

# Respond to ICMP
net.ipv4.icmp_echo_ignore_all = 1
net.ipv6.icmp.echo_ignore_all = 1

# Enable IP Forwarding
# Almost all of my servers run Docker anyways, and Docker absolutely requires this.
net.ipv4.ip_forward = 1
net.ipv6.conf.all.forwarding = 1

# https://www.stigviewer.com/stig/red_hat_enterprise_linux_6/2016-06-05/finding/V-38537
# Ignore bogus icmp response
net.ipv4.icmp_ignore_bogus_error_responses = 1

# Protection against time-wait assasination attacks
net.ipv4.tcp_rfc1337 = 1

# Enable SYN cookies
# Basic SYN flood mitigation
net.ipv4.tcp_syncookies = 1 

# https://access.redhat.com/sites/default/files/attachments/20150325_network_performance_tuning.pdf
# Make sure TCP timestamp is enabled
net.ipv4.tcp_timestamps = 1

# https://access.redhat.com/sites/default/files/attachments/20150325_network_performance_tuning.pdf
# Disable TCP SACK
# We have good networking :)
net.ipv4.tcp_sack = 0

# No SACK, therefore no Duplicated SACK
net.ipv4.tcp_dsack = 0

# Improve ALSR effectiveness for mmap
vm.mmap_rnd_bits = 32
vm.mmap_rnd_compat_bits = 16

# https://madaidans-insecurities.github.io/guides/linux-hardening.html#sysctl-kernel
# Restrict userfaultfd to CAP_SYS_PTRACE
# https://bugs.archlinux.org/task/62780
# Interestingly enough, Arch does not even have userfaultfd in their kernel, so it is
# probably not used in the real world at all.
vm.unprivileged_userfaultfd = 0