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Special Forums Cybersecurity Continual knocking on port 443 from foreign IP address Post 302893863 by Perderabo on Friday 21st of March 2014 11:26:36 AM
Old 03-21-2014
Quote:
Originally Posted by randomxs

Why would someone continually try to access the https port for months on end 100s of times an hour when clearly they must see they are being denied access to the server?


Iptables is not perfect and even when you use DROP rather than REJECT a port scanner can tell that DROP is in use by doing a SYN scan. If a server is on the port the SYN will get an ACK, otherwise it gets a RST. So the bad guy knows that he is getting nailed by a DROP rule and there is a live server being protected by the DROP rule. So he sets up an infinite loop trying to connect.

He hopes you will someday have a problem, wonder if iptables is causing it, and try dropping iptables just for a few seconds. Or maybe you will change your configuration and do a quick "service iptables restart". Most iptable configs allow ESTABLISHED connections to persist so once he connects... he is in.
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TCPDROP(8)						    BSD System Manager's Manual 						TCPDROP(8)

NAME
tcpdrop -- drop TCP connections SYNOPSIS
tcpdrop local-address local-port foreign-address foreign-port tcpdrop [-l] -a DESCRIPTION
The tcpdrop command may be used to drop TCP connections from the command line. If -a is specified then tcpdrop will attempt to drop all active connections. The -l flag may be given to list the tcpdrop invocation to drop all active connections one at a time. If -a is not specified then only the connection between the given local address local-address, port local-port, and the foreign address foreign-address, port foreign-port, will be dropped. Addresses and ports may be specified by name or numeric value. Both IPv4 and IPv6 address formats are supported. The addresses and ports may be separated by periods or colons instead of spaces. EXIT STATUS
The tcpdrop utility exits 0 on success, and >0 if an error occurs. EXAMPLES
If a connection to httpd(8) is causing congestion on a network link, one can drop the TCP session in charge: # sockstat -c | grep httpd www httpd 16525 3 tcp4 192.168.5.41:80 192.168.5.1:26747 The following command will drop the connection: # tcpdrop 192.168.5.41 80 192.168.5.1 26747 The following command will drop all connections but those to or from port 22, the port used by sshd(8): # tcpdrop -l -a | grep -vw 22 | sh SEE ALSO
netstat(1), sockstat(1) AUTHORS
Markus Friedl <markus@openbsd.org> Juli Mallett <jmallett@FreeBSD.org> BSD
January 30, 2013 BSD
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