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

# https://access.redhat.com/solutions/1985633
# Seems dangerous.
# Roseta need this though, so if you use it change it to 1.
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 a workstation, this shouldn't be used at all. Don't live patch, just reboot.
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

# Needed for Flatpak and Bubblewrap.
kernel.unprivileged_userns_clone = 1

# Disable ptrace. Not needed on workstations.
kernel.yama.ptrace_scope = 3

# 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

# Disable io_uring
# https://docs.kernel.org/admin-guide/sysctl/kernel.html#io-uring-disabled
# https://security.googleblog.com/2023/06/learnings-from-kctf-vrps-42-linux.html
# Note that this will make using Proxmox extremely annoying though, so you might wanna comment this out
# on a Proxmox node.
kernel.io_uring_disabled = 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

# Do not respond to ICMP.
net.ipv4.icmp_echo_ignore_all = 1
net.ipv6.icmp.echo_ignore_all = 1

# Ignore Bogus ICMP responses.
net.ipv4.icmp_ignore_bogus_error_responses = 1

# Enable IP Forwarding.
# Needed for VM networking and whatnot.
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