Eu tenho um servidor com postfix / dovecot que de alguma forma está sendo atacado. Eu constantemente vejo uma quantidade enorme de logs como este (substituído meu domínio por example.com):
Jul 2 10:03:03 my-server postfix/pickup[14702]: 878D313894B: uid=33 from=<www-data>
Jul 2 10:03:03 my-server postfix/cleanup[14916]: 878D313894B: message-id=<[email protected]>
Jul 2 10:03:03 my-server postfix/qmgr[19570]: 878D313894B: from=<[email protected]>, size=40324, nrcpt=1 (queue active)
Jul 2 10:03:05 my-server postfix/smtp[14923]: 878D313894B: to=<[email protected]>, relay=hotmail-com.olc.protection.outlook.com[104.47.42.33]:25, delay=2.1, delays=0.03/0.03/1.1/0.93, dsn=2.6.0, status=sent (250 2.6.0 <[email protected]> [InternalId=11360188501262, Hostname=BY2NAM03HT083.eop-NAM03.prod.protection.outlook.com] 45866 bytes in 0.498, 89.854 KB/sec Queued mail for delivery)
Jul 2 10:03:05 my-server postfix/qmgr[19570]: 878D313894B: removed
Jul 2 10:03:03 my-server postfix/pickup[14702]: 97D4E138950: uid=33 from=<www-data>
Jul 2 10:03:03 my-server postfix/cleanup[14916]: 97D4E138950: message-id=<[email protected]>
Jul 2 10:03:03 my-server postfix/qmgr[19570]: 97D4E138950: from=<[email protected]>, size=40308, nrcpt=1 (queue active)
Jul 2 10:03:03 my-server postfix/smtp[14933]: 97D4E138950: to=<a@a>, relay=none, delay=0.14, delays=0.01/0.02/0.11/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=a type=AAAA: Host not found)
Jul 2 10:03:03 my-server postfix/bounce[14935]: 97D4E138950: sender non-delivery notification: B9416138951
Jul 2 10:03:03 my-server postfix/qmgr[19570]: 97D4E138950: removed
Jul 2 10:03:03 my-server postfix/cleanup[14916]: A6851138951: message-id=<[email protected]>
Jul 2 10:03:03 my-server postfix/qmgr[19570]: A6851138951: from=<>, size=42121, nrcpt=1 (queue active)
Jul 2 10:03:03 my-server postfix/bounce[14935]: 9C33113894C: sender non-delivery notification: A6851138951
Jul 2 10:03:03 my-server dovecot: lmtp([email protected]): mNzcKTfcOVtZOgAAruHjSQ: msgid=<[email protected]>: saved mail to INBOX
Jul 2 10:03:03 my-server postfix/lmtp[14936]: A6851138951: to=<[email protected]>, orig_to=<[email protected]>, relay=example.com[private/dovecot-lmtp], delay=0.03, delays=0/0.01/0.01/0.01, dsn=2.0.0, status=sent (250 2.0.0 <[email protected]> mNzcKTfcOVtZOgAAruHjSQ Saved)
Jul 2 10:03:03 my-server postfix/qmgr[19570]: A6851138951: removed
Eu já tentei configurar o postfix com as seguintes regras para evitar esse tipo de ataque, ele acalmou a magnitude, mas o servidor ainda está recebendo uma quantidade enorme de atividade:
/etc/postfix/main.cf :
#################################################################
# ANTI SPAM: https://www.howtoforge.com/virtual_postfix_antispam
#################################################################
smtpd_helo_required = yes
strict_rfc821_envelopes = yes
disable_vrfy_command = yes
unknown_address_reject_code = 554
unknown_hostname_reject_code = 554
unknown_client_reject_code = 554
smtpd_sender_restrictions = reject_unknown_address
smtpd_helo_restrictions =
permit_mynetworks,
reject_invalid_hostname,
regexp:/etc/postfix/antispam/helo.regexp,
permit
#smtpd_recipient_restrictions =
# permit_sasl_authenticated,
# permit_mynetworks,
# reject_unauth_destination
smtpd_recipient_restrictions =
check_client_access hash:/etc/postfix/antispam/helo_client_exceptions
# check_sender_access hash:/etc/postfix/antispam/sender_checks,
reject_invalid_hostname,
### Can cause issues with Auth SMTP, so be weary!
reject_non_fqdn_hostname,
##################################
reject_non_fqdn_sender,
reject_non_fqdn_recipient,
reject_unknown_sender_domain,
reject_unknown_recipient_domain,
permit_mynetworks,
reject_unauth_destination,
# Add RBL exceptions here, when changing rbl_client_exceptions, this file must be regenerated using postmap <file>, to generate a Berkeley DB
check_client_access hash:/etc/postfix/antispam/rbl_client_exceptions,
reject_rbl_client cbl.abuseat.org,
# reject_rbl_client zen.spamhaus.org,
reject_rbl_client bl.spamcop.net,
# reject_rbl_client list.dsbl.org
reject_rhsbl_sender dsn.rfc-ignorant.org,
# check_policy_service inet:127.0.0.1:60000,
permit
smtpd_relay_restrictions =
permit_mynetworks,
# permit_sasl_authenticated,
defer_unauth_destination
Eu tenho medo que este servidor esteja sendo usado para de alguma forma enviar spam para as pessoas, por isso pode incomodar as pessoas e prejudicar minha reputação de IP.
Eu dediquei muitas horas investigando e lendo documentação na internet, mas ainda estou confuso sobre o que está acontecendo e como pará-lo. Eu gostaria de saber como o invasor está usando este servidor e como posso parar os ataques.
Não sei se está relacionado, hoje recebi um e-mail do meu provedor de hospedagem dizendo que eles suspenderam o servidor porque detectaram atividade incomum (duas vezes hoje, duas vezes há 15 dias):
Attack detail : 173Kpps/38Mbps
dateTime srcIp:srcPort dstIp:dstPort protocol flags bytes reason
2018.07.02 16:35:04 CEST xx.xx.xx.xx:41403 78.46.61.106:80 UDP --- 29 ATTACK:UDP
Fechei todas as portas, exceto TCP 22, 80, 443, 25, 587, 993, 995, 465, portanto, espero que o UDP de saída esteja bloqueado. Não tenho certeza se existe algum malware instalado no servidor que está acionando essa atividade e como detectá-lo.