DDoS Mitigation

Files

Zeroline This script automatically and safely installs all the iptables rules and kernel modifications that are in this repository instantly.
Download v1.0

Disclaimer

Some rules may interfere with the functioning of the tools and tips in this repository. Make sure you have an emergency method to disable the Firewall or revert the changes made with this repository in case you lose access to the server.

Index

• Kernel
  • Drop ICMP Echo Requests
  • Dont accept ICMP Redirect
  • Drop source routed packets
  • Enable SYN-Cookie (for prevent SYN Flood)
  • Increase TCP SYN backlog (for prevent TCP Starvation)
  • Decrease TCP SYN-ACK retries (for prevent TCP Starvation)
  • Enable Address Spoofing Protection
  • Disable SYN Packet tracking
• IPTables
  • Drop Invalid Packets
  • Block packets with bogus TCP flags
  • Drop ICMP
  • Drop Fragments in all Chains
  • Limit connections per IP
  • Limit RST Packets
  • Use of SYN-PROXY
  • Prevent SSH Bruteforce
  • Prevent Port Scanner

Kernel Modifications

Drop ICMP ECHO-Requests

To prevent smurf attack.

echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

Dont accept ICMP Redirect

To prevent smurf attack.

echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects

Drop source routed packets

echo 0 > /proc/sys/net/ipv4/conf/all/accept_source_route

Enable SYN-Cookie for prevent SYN Flood

To prevent SYN Flood and TCP Starvation.

sysctl -w net/ipv4/tcp_syncookies=1
sysctl -w net/ipv4/tcp_timestamps=1

Increase TCP SYN backlog

To prevent TCP Starvation.

echo 2048 > /proc/sys/net/ipv4/tcp_max_syn_backlog

Decrease TCP SYN-ACK retries

To prevent TCP Starvation.

echo 3 > /proc/sys/net/ipv4/tcp_synack_retries

Enable Address Spoofing Protection

To prevent IP Spoof.

echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter

Disable SYN Packet tracking

To prevent the system from using resources tracking SYN Packets.

sysctl -w net/netfilter/nf_conntrack_tcp_loose=0

IPTables

Drop Invalid Packets

Drop invalid packets with invalid or unknown status.

iptables -A INPUT -m state --state INVALID -j DROP

Block packets with bogus TCP flags

iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,RST FIN,RST -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,ACK FIN -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,URG URG -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,FIN FIN -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,PSH PSH -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL ALL -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL NONE -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL FIN,PSH,URG -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL SYN,FIN,PSH,URG -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP

Drop ICMP

To prevent Smurf Attack.

iptables -t mangle -A PREROUTING -p icmp -j DROP

Drop Fragments in all Chains

iptables -t mangle -A PREROUTING -f -j DROP

Limit connections per IP

iptables -A INPUT -p tcp -m connlimit --connlimit-above 111 -j REJECT --reject-with tcp-reset

Limit RST Packets

iptables -A INPUT -p tcp --tcp-flags RST RST -m limit --limit 2/s --limit-burst 2 -j ACCEPT
iptables -A INPUT -p tcp --tcp-flags RST RST -j DROP

Use of SYN-PROXY

iptables -t raw -A PREROUTING -p tcp -m tcp --syn -j CT --notrack
iptables -A INPUT -p tcp -m tcp -m conntrack --ctstate INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460
iptables -A INPUT -m state --state INVALID -j DROP

Prevent SSH Bruteforce

iptables -A INPUT -p tcp --dport ssh -m conntrack --ctstate NEW -m recent --set
iptables -A INPUT -p tcp --dport ssh -m conntrack --ctstate NEW -m recent --update --seconds 60 --hitcount 10 -j DROP

Prevent Port Scanner

iptables -N port-scanning
iptables -A port-scanning -p tcp --tcp-flags SYN,ACK,FIN,RST RST -m limit --limit 1/s --limit-burst 2 -j RETURN
iptables -A port-scanning -j DROP

Sources

• hackplayers.com
• stackexchange.com