# Linux Kernel Security Hardening
# Place in /etc/sysctl.d/99-security.conf
# Apply with: sysctl -p /etc/sysctl.d/99-security.conf

#------------------------------------------------------------------------------
# NETWORK SECURITY
#------------------------------------------------------------------------------

# Disable IP forwarding (unless router)
net.ipv4.ip_forward = 0
net.ipv6.conf.all.forwarding = 0

# Disable packet redirect sending
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0

# Disable ICMP redirect acceptance
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0
net.ipv6.conf.all.accept_redirects = 0
net.ipv6.conf.default.accept_redirects = 0

# Disable source routing
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv6.conf.all.accept_source_route = 0
net.ipv6.conf.default.accept_source_route = 0

# Log suspicious packets
net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.default.log_martians = 1

# Ignore ICMP broadcast requests
net.ipv4.icmp_echo_ignore_broadcasts = 1

# Ignore bogus ICMP error responses
net.ipv4.icmp_ignore_bogus_error_responses = 1

# Enable reverse path filtering (spoofing protection)
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1

# Enable TCP SYN cookies (SYN flood protection)
net.ipv4.tcp_syncookies = 1

# Disable IPv6 router advertisements
net.ipv6.conf.all.accept_ra = 0
net.ipv6.conf.default.accept_ra = 0

# Disable IPv6 if not needed
# net.ipv6.conf.all.disable_ipv6 = 1
# net.ipv6.conf.default.disable_ipv6 = 1

#------------------------------------------------------------------------------
# KERNEL SECURITY
#------------------------------------------------------------------------------

# Enable ASLR
kernel.randomize_va_space = 2

# Restrict access to kernel pointers
kernel.kptr_restrict = 2

# Restrict dmesg access
kernel.dmesg_restrict = 1

# Restrict ptrace scope
kernel.yama.ptrace_scope = 1

# Disable magic SysRq key
kernel.sysrq = 0

# Restrict unprivileged user namespaces
# kernel.unprivileged_userns_clone = 0

# Restrict loading TTY line disciplines
dev.tty.ldisc_autoload = 0

# Restrict userfaultfd to privileged users
vm.unprivileged_userfaultfd = 0

# Restrict BPF
kernel.unprivileged_bpf_disabled = 1
net.core.bpf_jit_harden = 2

# Restrict perf events
kernel.perf_event_paranoid = 3

#------------------------------------------------------------------------------
# FILE SYSTEM SECURITY
#------------------------------------------------------------------------------

# Restrict core dumps
fs.suid_dumpable = 0

# Restrict hardlinks and symlinks
fs.protected_hardlinks = 1
fs.protected_symlinks = 1

# Protect FIFOs and regular files
fs.protected_fifos = 2
fs.protected_regular = 2