Following script will protect collocated FreeBSD / OpenBSD / NetBSD server running PF firewall. My box has 2 interface one for VPN and other for public interface. I only run http, dns and ssh on public port. Read pf, rc.conf and pf.conf man page for details. Tested on FreeBSD and OpenBSD.
Sample /etc/pf.conf
#### First declare a couple of variables #### ### Outgoing tcp / udp port #### ### 43 - whois, 22 - ssh ### tcp_services = "{ ssh, smtp, domain, www, https, 22, ntp, 43,ftp, ftp-data}" udp_services = "{ domain, ntp }" ### allow ping / pong #### icmp_types = "{ echoreq, unreach }" #### define tables. add all subnets and ips to block table <blockedip> persist file "/etc/pf.block.ip.conf" martians = "{ 127.0.0.0/8, 192.168.0.0/16, 172.16.0.0/12, 10.0.0.0/8, 169.254.0.0/16, 192.0.2.0/24, 0.0.0.0/8, 240.0.0.0/4 }" ### admin server ranges ### adminrange = "112.220.11.0/23" # connected to internet ext_if = "em1" # connected to vpn / lan int_if = "em0" ##### ftp proxy #proxy="127.0.0.1" #proxyport="8021" #### Normalization #scrub provides a measure of protection against certain kinds of attacks based on incorrect handling of packet fragments scrub in all #### NAT and RDR start #nat-anchor "ftp-proxy/*" #rdr-anchor "ftp-proxy/*" # redirect ftp traffic #rdr pass proto tcp from any to any port ftp -> $proxy port $proxyport # Drop incoming everything block in all block return # keep stats of outgoing connections pass out keep state # We need to have an anchor for ftp-proxy #anchor "ftp-proxy/*" # unlimited traffic for loopback and lan / vpn set skip on {lo0, $int_if} # activate spoofing protection for all interfaces block in quick from urpf-failed #antispoof is a common special case of filtering and blocking. This mechanism protects against activity from spoofed or forged IP addresses antispoof log for $ext_if #Block RFC 1918 addresses block drop in log (all) quick on $ext_if from $martians to any block drop out log (all) quick on $ext_if from any to $martians # Block all ips # pfctl -t blockedip -T show block drop in log (all) quick on $ext_if from <blockedip> to any block drop out log (all) quick on $ext_if from any to <blockedip> # allow outgoing pass out on $ext_if proto tcp to any port $tcp_services pass out on $ext_if proto udp to any port $udp_services # Allow trace route pass out on $ext_if inet proto udp from any to any port 33433 >< 33626 keep state # Allow admin to get into box pass in on $int_if from $adminrange to any # Allow incoming ssh, http, bind traffic # pass in on $ext_if proto tcp from any to any port 25 pass in on $ext_if proto tcp from any to any port ssh flags S/SA synproxy state pass in on $ext_if proto udp from any to any port domain pass in on $ext_if proto tcp from any to any port domain flags S/SA synproxy state pass in on $ext_if proto tcp from any to any port http flags S/SA synproxy modulate state pass inet proto icmp all icmp-type $icmp_types keep state ## add your rule below ##
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| Category | List of Unix and Linux commands |
|---|---|
| File Management | cat |
| Firewall | CentOS 8 • OpenSUSE • RHEL 8 • Ubuntu 16.04 • Ubuntu 18.04 • Ubuntu 20.04 |
| Network Utilities | dig • host • ip • nmap |
| OpenVPN | CentOS 7 • CentOS 8 • Debian 10 • Debian 8/9 • Ubuntu 18.04 • Ubuntu 20.04 |
| Package Manager | apk • apt |
| Processes Management | bg • chroot • cron • disown • fg • jobs • killall • kill • pidof • pstree • pwdx • time |
| Searching | grep • whereis • which |
| User Information | groups • id • lastcomm • last • lid/libuser-lid • logname • members • users • whoami • who • w |
| WireGuard VPN | CentOS 8 • Debian 10 • Firewall • Ubuntu 20.04 |
You probably don’t want to block all the other icmp types like fragmentation-needed – it breaks things in a subtle but annoying way!
pass quick proto tcp from $table to $ext_if port 22 flags S/SA keep state
and if you want ssh brute force options;
table persist file “/etc/bruteforce.conf”
pass quick proto tcp from $table to $ext_if port 22 flags S/SA keep state (max-src-conn 15, max-src-conn-rate 5/3, overload flush global)
And I think we should use
Hi, CMIIW but this rule:
pass out keep statejust makes this rules:
pass out on $ext_if proto tcp to any port $tcp_services pass out on $ext_if proto udp to any port $udp_servicesa bit pointless? I’m still able to connect to any ports.
How can i block port 22 to public and give permission to specific ip address
here is what I have done
## ips ok for sshtable { 1.2.3.4, 5.6.7.8, 9.10.11.12 }# and thenpass in on $ext_iface proto tcp from to any port 22 flags S/SA synproxy stateIt is ok. Simple and great.
Normally, a client connects to the server and we handshake with them, then proceed to exchange data. by telling pf to handshake proxy between the client and server, tcp syn flood attacts from ddos become uneffective because a spoofed client cannot complete a handshake.
As Dirk Gently says: More comments are welcome.
Yes, it was a typo. Thanks for the heads-up!
oops, i think the problem might be
pass in on $ext_if proto tcp from ant to any port ssh flags S/SA synproxy state
“ant” should be “any” ?
freebsd 7.2-RELEASE – I believe it ships with pf @ OpenBSD 4.1
notes:
1) “$ext_if proto tcp from any to any port http flags S/SA synproxy modulate state”
throws me a syntax error, I understand that using synproxy and modulate is redundant, ie synproxy includes modulate and keep.
2) using synproxy with ssh ain’t happening for me, not yet sure – researching.
3) in pf @ OpenBSD 4.1, default TCP flags are S/SA keep state
thanks, keep up the great work.
# synproxy state – proxies incoming TCP connections to help protect servers from spoofed TCP SYN floods. This option includes the functionality of keep state and modulate state.
Good work vivec. great help when pf.conf is lacking comments. ;)
This was very helpful :) Thank You ;-)
Regards
http://hekko.eu