Veo paredes de troncos como este en /var/log/auth.log. Cada 2 minutos aparecen diez líneas del mismo mensaje. Me gustaría saber la IP remota que generó estos mensajes.
Estoy ejecutando Ubuntu 19.10 (es mi estación de trabajo remota, solo hago comprobaciones de seguridad periódicas)
61094 Jan 25 22:44:01 localhost sshd[10390]: error: kex_exchange_identification: Connection closed by remote host
61095 Jan 25 22:44:02 localhost sshd[10408]: error: kex_exchange_identification: Connection closed by remote host
61096 Jan 25 22:44:02 localhost sshd[10433]: error: kex_exchange_identification: Connection closed by remote host
61097 Jan 25 22:44:02 localhost sshd[10437]: error: kex_exchange_identification: Connection closed by remote host
61098 Jan 25 22:44:02 localhost sshd[10441]: error: kex_exchange_identification: Connection closed by remote host
61099 Jan 25 22:44:02 localhost sshd[10446]: error: kex_exchange_identification: Connection closed by remote host
61100 Jan 25 22:44:02 localhost sshd[10450]: error: kex_exchange_identification: Connection closed by remote host
61101 Jan 25 22:44:02 localhost sshd[10454]: error: kex_exchange_identification: Connection closed by remote host
61102 Jan 25 22:44:02 localhost sshd[10462]: error: kex_exchange_identification: Connection closed by remote host
61103 Jan 25 22:44:02 localhost sshd[10466]: error: kex_exchange_identification: Connection closed by remote host
61104 Jan 25 22:46:01 localhost sshd[12501]: error: kex_exchange_identification: Connection closed by remote host
61105 Jan 25 22:46:01 localhost sshd[12528]: error: kex_exchange_identification: Connection closed by remote host
61106 Jan 25 22:46:01 localhost sshd[12538]: error: kex_exchange_identification: Connection closed by remote host
61107 Jan 25 22:46:01 localhost sshd[12542]: error: kex_exchange_identification: Connection closed by remote host
61108 Jan 25 22:46:01 localhost sshd[12546]: error: kex_exchange_identification: Connection closed by remote host
61109 Jan 25 22:46:01 localhost sshd[12551]: error: kex_exchange_identification: Connection closed by remote host
61110 Jan 25 22:46:01 localhost sshd[12555]: error: kex_exchange_identification: Connection closed by remote host
61111 Jan 25 22:46:01 localhost sshd[12560]: error: kex_exchange_identification: Connection closed by remote host
61112 Jan 25 22:46:01 localhost sshd[12564]: error: kex_exchange_identification: Connection closed by remote host
61113 Jan 25 22:46:01 localhost sshd[12568]: error: kex_exchange_identification: Connection closed by remote host
61114 Jan 25 22:48:01 localhost sshd[14371]: error: kex_exchange_identification: Connection closed by remote host
61115 Jan 25 22:48:01 localhost sshd[14390]: error: kex_exchange_identification: Connection closed by remote host
61116 Jan 25 22:48:01 localhost sshd[14414]: error: kex_exchange_identification: Connection closed by remote host
61117 Jan 25 22:48:01 localhost sshd[14418]: error: kex_exchange_identification: Connection closed by remote host
61118 Jan 25 22:48:01 localhost sshd[14422]: error: kex_exchange_identification: Connection closed by remote host
61119 Jan 25 22:48:01 localhost sshd[14427]: error: kex_exchange_identification: Connection closed by remote host
61120 Jan 25 22:48:01 localhost sshd[14431]: error: kex_exchange_identification: Connection closed by remote host
61121 Jan 25 22:48:01 localhost sshd[14435]: error: kex_exchange_identification: Connection closed by remote host
61122 Jan 25 22:48:01 localhost sshd[14439]: error: kex_exchange_identification: Connection closed by remote host
61123 Jan 25 22:48:01 localhost sshd[14443]: error: kex_exchange_identification: Connection closed by remote host
61124 Jan 25 22:50:01 localhost sshd[16489]: error: kex_exchange_identification: Connection closed by remote host
61125 Jan 25 22:50:01 localhost sshd[16512]: error: kex_exchange_identification: Connection closed by remote host
61126 Jan 25 22:50:01 localhost sshd[16530]: error: kex_exchange_identification: Connection closed by remote host
61127 Jan 25 22:50:01 localhost sshd[16535]: error: kex_exchange_identification: Connection closed by remote host
61128 Jan 25 22:50:01 localhost sshd[16539]: error: kex_exchange_identification: Connection closed by remote host
61129 Jan 25 22:50:01 localhost sshd[16544]: error: kex_exchange_identification: Connection closed by remote host
61130 Jan 25 22:50:01 localhost sshd[16548]: error: kex_exchange_identification: Connection closed by remote host
61131 Jan 25 22:50:01 localhost sshd[16552]: error: kex_exchange_identification: Connection closed by remote host
61132 Jan 25 22:50:01 localhost sshd[16556]: error: kex_exchange_identification: Connection closed by remote host
61133 Jan 25 22:50:01 localhost sshd[16561]: error: kex_exchange_identification: Connection closed by remote host
61134 Jan 25 22:52:01 localhost sshd[18480]: error: kex_exchange_identification: Connection closed by remote host
61135 Jan 25 22:52:01 localhost sshd[18491]: error: kex_exchange_identification: Connection closed by remote host
61136 Jan 25 22:52:01 localhost sshd[18518]: error: kex_exchange_identification: Connection closed by remote host
61137 Jan 25 22:52:01 localhost sshd[18523]: error: kex_exchange_identification: Connection closed by remote host
61138 Jan 25 22:52:01 localhost sshd[18527]: error: kex_exchange_identification: Connection closed by remote host
61139 Jan 25 22:52:01 localhost sshd[18532]: error: kex_exchange_identification: Connection closed by remote host
61140 Jan 25 22:52:01 localhost sshd[18536]: error: kex_exchange_identification: Connection closed by remote host
auth.log-20200126-1579968001 61140,1 99%
Respuesta1
Intente ejecutar tcpdumpen su sshpuerto:
tcpdump -nn -s0 port 22
Si ya inició sesión en ssh, excluya su dirección IP de origen (por ejemplo: 203.202.1.1) para no inundar su terminal con su propio tráfico:
tcpdump -nn -s0 port 22 and not src 203.202.1.1 and not dst 203.202.1.1
También puede usar Netfilter para registrar conexiones en syslog, pero tenga en cuenta que una avalancha de conexiones puede crear suficiente carga en su servidor como para que deje de responder, por lo que no es algo que desee ejecutar sin ponerle algún tipo de límite de registro (como se muestra). :
iptables -I INPUT -p tcp --dport 22 -m limit --limit 4/min --limit-burst 4 -j LOG --log-prefix "SSH_NOTIFY: "
Esto mostrará un mensaje en su syslog sobre el host que se está conectando.
Respuesta2
verifique los permisos en el directorio /, debería ser algo como
drwxr-sr-x 1 root root 512 Feb 12 21:12