Tentei criar iptablesregras para evitar que o limite de conexões do meu servidor seja preenchido com pacotes SYN incompletos para os quais nenhum pacote ACK é retornado pelo cliente (ataque de inundação SYN).
Eu li o [RFC 4987 TCP SYN Flooding Attacks and Common Mitigations][1] e [Mitigate TCP SYN Flood Attacks with Red Hat Enterprise Linux 7 Beta][2] e finalmente tentei seguir as instruções [aqui][3]:https://javapipe.com/blog/iptables-ddos-protection/
No entanto, meu site ainda é facilmente derrubado por um ataque DOS usando o seguinte comando:
hping -S --flood -V -p 443 www.mydomain.com
No final do tutorial do Javapipe.com vinculado acima, o comando é mencionado para informar se SYNPROXY está ativo ou não.
Para verificar se o SYNPROXY está funcionando, você pode fazer watch -n1 cat /proc/net/stat/synproxy. Se os valores mudarem quando você estabelecer uma nova conexão TCP com a porta em que usa SYNPROXY, isso funcionará.
O comando é:
watch -n1 cat /proc/net/stat/synproxy
Quando uso esse comando no meu servidor e tento carregar uma página, os dados não mudam e são todos zeros.
Every 1.0s: cat /proc/net/stat/synproxy Thu Jul 25 19:57:00 2019
entries syn_received cookie_invalid cookie_valid cookie_retrans conn_reopened
00000000 00000000 00000000 00000000 00000000 00000000
Aqui está a saída do iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED
ACCEPT all -- anywhere anywhere
INPUT_direct all -- anywhere anywhere
INPUT_ZONES_SOURCE all -- anywhere anywhere
INPUT_ZONES all -- anywhere anywhere
REJECT all -- anywhere anywhere reject-with icmp-host-prohibited
REJECT tcp -- anywhere anywhere #conn src/32 > 80 reject-with tcp-reset
ACCEPT tcp -- anywhere anywhere ctstate NEW limit: avg 20/sec burst 20
DROP tcp -- anywhere anywhere ctstate NEW
ACCEPT tcp -- anywhere anywhere tcp flags:RST/RST limit: avg 2/sec burst 2
DROP tcp -- anywhere anywhere tcp flags:RST/RST
DROP all -- anywhere anywhere ctstate INVALID
SYNPROXY tcp -- anywhere anywhere tcp ctstate INVALID,UNTRACKED SYNPROXY sack-perm timestamp wscale 7 mss 1460
DROP all -- anywhere anywhere ctstate INVALID
DROP all -- anywhere anywhere state INVALID
Chain FORWARD (policy ACCEPT)
target prot opt source destination
ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED
ACCEPT all -- anywhere anywhere
FORWARD_direct all -- anywhere anywhere
FORWARD_IN_ZONES_SOURCE all -- anywhere anywhere
FORWARD_IN_ZONES all -- anywhere anywhere
FORWARD_OUT_ZONES_SOURCE all -- anywhere anywhere
FORWARD_OUT_ZONES all -- anywhere anywhere
DROP all -- anywhere anywhere ctstate INVALID
REJECT all -- anywhere anywhere reject-with icmp-host-prohibited
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
OUTPUT_direct all -- anywhere anywhere
Chain FORWARD_IN_ZONES (1 references)
target prot opt source destination
FWDI_public all -- anywhere anywhere [goto]
Chain FORWARD_IN_ZONES_SOURCE (1 references)
target prot opt source destination
Chain FORWARD_OUT_ZONES (1 references)
target prot opt source destination
FWDO_public all -- anywhere anywhere [goto]
Chain FORWARD_OUT_ZONES_SOURCE (1 references)
target prot opt source destination
Chain FORWARD_direct (1 references)
target prot opt source destination
Chain FWDI_public (1 references)
target prot opt source destination
FWDI_public_log all -- anywhere anywhere
FWDI_public_deny all -- anywhere anywhere
FWDI_public_allow all -- anywhere anywhere
REJECT icmp -- anywhere anywhere reject-with icmp-host-prohibited
Chain FWDI_public_allow (1 references)
target prot opt source destination
Chain FWDI_public_deny (1 references)
target prot opt source destination
Chain FWDI_public_log (1 references)
target prot opt source destination
Chain FWDO_public (1 references)
target prot opt source destination
FWDO_public_log all -- anywhere anywhere
FWDO_public_deny all -- anywhere anywhere
FWDO_public_allow all -- anywhere anywhere
Chain FWDO_public_allow (1 references)
target prot opt source destination
Chain FWDO_public_deny (1 references)
target prot opt source destination
Chain FWDO_public_log (1 references)
target prot opt source destination
Chain INPUT_ZONES (1 references)
target prot opt source destination
IN_public all -- anywhere anywhere [goto]
Chain INPUT_ZONES_SOURCE (1 references)
target prot opt source destination
Chain INPUT_direct (1 references)
target prot opt source destination
Chain IN_public (1 references)
target prot opt source destination
IN_public_log all -- anywhere anywhere
IN_public_deny all -- anywhere anywhere
IN_public_allow all -- anywhere anywhere
REJECT icmp -- anywhere anywhere reject-with icmp-host-prohibited
Chain IN_public_allow (1 references)
target prot opt source destination
ACCEPT tcp -- anywhere anywhere tcp dpt:ssh ctstate NEW
ACCEPT tcp -- anywhere anywhere tcp dpt:http ctstate NEW
ACCEPT tcp -- anywhere anywhere tcp dpt:https ctstate NEW
ACCEPT tcp -- anywhere anywhere tcp dpt:smtp ctstate NEW
Chain IN_public_deny (1 references)
target prot opt source destination
Chain IN_public_log (1 references)
target prot opt source destination
Chain OUTPUT_direct (1 references)
target prot opt source destination
O servidor é um VPS com Digital Ocean rodando Centos 7.6, Kernel: 3.10.0-862.2.3.el7.x86_64
Alguém pode ajudar a explicar por que o SYNPROXY pode não estar em execução, ou então, por que/como proteger meu servidor contra inundação de SYN?