snowflake/modules/security.nix

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# security tweaks borrowed from @hlissner
{
boot.kernel.sysctl = {
# The Magic SysRq key is a key combo that allows users connected to the
# system console of a Linux kernel to perform some low-level commands.
# Disable it, since we don't need it, and is a potential security concern.
"kernel.sysrq" = 0;
## TCP hardening
# Prevent bogus ICMP errors from filling up logs.
"net.ipv4.icmp_ignore_bogus_error_responses" = 1;
# Reverse path filtering causes the kernel to do source validation of
# packets received from all interfaces. This can mitigate IP spoofing.
"net.ipv4.conf.default.rp_filter" = 1;
"net.ipv4.conf.all.rp_filter" = 1;
# Do not accept IP source route packets (we're not a router)
"net.ipv4.conf.all.accept_source_route" = 0;
"net.ipv6.conf.all.accept_source_route" = 0;
# Don't send ICMP redirects (again, we're on a router)
"net.ipv4.conf.all.send_redirects" = 0;
"net.ipv4.conf.default.send_redirects" = 0;
# Refuse ICMP redirects (MITM mitigations)
"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;
# Protects against SYN flood attacks
"net.ipv4.tcp_syncookies" = 1;
# Incomplete protection again TIME-WAIT assassination
"net.ipv4.tcp_rfc1337" = 1;
## TCP optimization
# TCP Fast Open is a TCP extension that reduces network latency by packing
# data in the senders initial TCP SYN. Setting 3 = enable TCP Fast Open for
# both incoming and outgoing connections:
"net.ipv4.tcp_fastopen" = 3;
# Bufferbloat mitigations + slight improvement in throughput & latency
"net.ipv4.tcp_congestion_control" = "bbr";
"net.core.default_qdisc" = "cake";
};
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boot.kernelModules = ["tcp_bbr"];
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services.openssh.settings.LogLevel = "VERBOSE";
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security.acme = {
acceptTerms = true;
defaults.email = "github@notohh.dev";
};
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services.fail2ban = {
enable = true;
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bantime = "1h";
maxretry = 1;
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ignoreIP = [
"192.168.0.0/16"
"172.16.0.0/12"
"10.0.0.0/8"
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"5.161.102.107/32"
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"100.71.49.65/10"
"100.82.146.40/10"
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];
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jails = {
DEFAULT = {
settings = {
findtime = 100000;
mode = "aggressive";
};
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};
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};
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};
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}