We recently received a notice from our Server-providers that they detected an outgoing port-scan from our Server. They checked for malware or compromised account, but didn't find any. All they have suggested is to add IpTables rule for outgoing TCP connections for 80 & 443.
But I would like to know what went wrong. Nothing in /var/log/auth.log. I have fail2ban also installed. Any ideas what I should do. Thanks a lot. :-)
Update
tcpdump on range 4000-8000.
tcpdump portrange 4000-8000
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
14:06:45.025204 IP pacific1660.serverprofi24.eu.5142 > static.126.53.251.148.clients.your-server.de.sip: SIP, length: 417
14:06:45.154178 IP pacific1660.serverprofi24.eu.5142 > legion04.delink-server.net.sip: SIP, length: 419
14:06:45.201135 IP pacific1660.serverprofi24.eu.5142 > static.158.53.251.148.clients.your-server.de.sip: SIP, length: 419
14:16:52.536090 IP 5.45.64.228.7835 > static.158.53.251.148.clients.your-server.de.https: Flags [S], seq 1603658319, win 29200, options [mss 1460], length 0
14:22:13.722644 IP scan-11d.shadowserver.org.45417 > legion04.delink-server.net.6379: Flags [S], seq 1826412023, win 65535, length 0
14:22:13.722660 IP legion04.delink-server.net.6379 > scan-11d.shadowserver.org.45417: Flags [R.], seq 0, ack 1826412024, win 0, length 0
Is the seq number used by shadowserver.org as high as 1826412023
normal? As I checked their site, they are for fighting cyber-crime.
tcpdump
.