I'm scanning a server which should have a pretty simple firewall using iptables: by default everything is DROPped besides RELATED
and ESTABLISHED
packets. The only type of NEW
packets allowed are TCP packets on port 22 and 80 and that's it (no HTTPS on that server).
The result of nmap on the first 2048 ports gives 22 and 80 as open, as I expect. However a few ports appear as "filtered".
My question is: why do port 21, 25 and 1863 appear as "filtered" and the 2043 other ports do not appear as filtered?
I expected to see only 22 and 80 as "open".
If it's normal to see 21,25 and 1863 as "filtered", then why aren't all the other ports appearing as "filtered" too!?
Here's the nmap output:
# nmap -PN 94.xx.yy.zz -p1-2048
Starting Nmap 6.00 ( http://nmap.org ) at 2014-06-12 ...
Nmap scan report for ksXXXXXX.kimsufi.com (94.xx.yy.zz)
Host is up (0.0023s latency).
Not shown: 2043 closed ports
PORT STATE SERVICE
21/tcp filtered ftp
22/tcp open ssh
25/tcp filtered smtp
80/tcp open http
1863/tcp filtered msnp
I really don't get why I have 2043 closed ports:
Not shown: 2043 closed ports
and not 2046 closed ports.
Here's an lsof launched on the server:
# lsof -i -n
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
named 3789 bind 20u IPv4 7802 TCP 127.0.0.1:domain (LISTEN)
named 3789 bind 21u IPv4 7803 TCP 127.0.0.1:953 (LISTEN)
named 3789 bind 512u IPv4 7801 UDP 127.0.0.1:domain
sshd 3804 root 3u IPv4 7830 TCP *:ssh (LISTEN)
sshd 5408 root 3r IPv4 96926113 TCP 94.xx.yy.zz:ssh->aa.bb.cc.dd:37516 (ESTABLISHED)
sshd 5411 b 3u IPv4 96926113 TCP 94.xx.yy.zz:ssh->aa.bb.cc.dd:37516 (ESTABLISHED)
java 16589 t 42u IPv4 88842753 TCP *:http-alt (LISTEN)
java 16589 t 50u IPv4 88842759 TCP *:8009 (LISTEN)
java 16589 t 51u IPv4 88842762 TCP 127.0.0.1:8005 (LISTEN)
(note that Java / Tomcat is listening on port 8009 but that port is DROPped by the firewall)
nmap
is doing you should be scanning using root privs, using the SYN scan (-sS
) and--packet-trace
. Also take a couple minutes and read the man page, you'd be surprised what gems are in there