Cannot close Port 25 after installing postfix

Question

Before installing logwatch (which installs postfix) on Ubuntu 12.04, the port 25 is blocked by iptables/csf

PORT   STATE    SERVICE
25/tcp filtered smtp

After installing logwatch (which installs postfix), port 25 is now opened

PORT   STATE SERVICE
25/tcp open  smtp

Restarted CSF using csf -r but the port remains open. Aren't all ports blocked by default except for those defined in TCP_ON, TCP_OUT, UDP_IN, UDP_OUT? Why is port 25 still open?

csf.conf

TCP_IN = "22,27017,27018,27019"
TCP_OUT = "53,27017,27018,27019"

UDP_IN = ""
UDP_OUT = "53,123"

sudo netstat -tnlp | grep :25

tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      7641/master     
tcp6       0      0 :::25                   :::*                    LISTEN      7641/master

iptables -L -n -v --line-numbers

Chain INPUT (policy DROP 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 ACCEPT     tcp  --  !lo    *       209.244.0.3          0.0.0.0/0            tcp dpt:53
2        0     0 ACCEPT     udp  --  !lo    *       209.244.0.3          0.0.0.0/0            udp dpt:53
3        0     0 ACCEPT     tcp  --  !lo    *       209.244.0.3          0.0.0.0/0            tcp spt:53
4        0     0 ACCEPT     udp  --  !lo    *       209.244.0.3          0.0.0.0/0            udp spt:53
5        0     0 ACCEPT     tcp  --  !lo    *       8.8.8.8              0.0.0.0/0            tcp dpt:53
6        0     0 ACCEPT     udp  --  !lo    *       8.8.8.8              0.0.0.0/0            udp dpt:53
7        0     0 ACCEPT     tcp  --  !lo    *       8.8.8.8              0.0.0.0/0            tcp spt:53
8        0     0 ACCEPT     udp  --  !lo    *       8.8.8.8              0.0.0.0/0            udp spt:53
9        0     0 ACCEPT     tcp  --  !lo    *       8.8.4.4              0.0.0.0/0            tcp dpt:53
10       0     0 ACCEPT     udp  --  !lo    *       8.8.4.4              0.0.0.0/0            udp dpt:53
11       0     0 ACCEPT     tcp  --  !lo    *       8.8.4.4              0.0.0.0/0            tcp spt:53
12      52  6331 ACCEPT     udp  --  !lo    *       8.8.4.4              0.0.0.0/0            udp spt:53
13   10491  986K LOCALINPUT  all  --  !lo    *       0.0.0.0/0            0.0.0.0/0           
14      51  3795 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0           
15   10278  968K INVALID    tcp  --  !lo    *       0.0.0.0/0            0.0.0.0/0           
16   10226  965K ACCEPT     all  --  !lo    *       0.0.0.0/0            0.0.0.0/0            ctstate RELATED,ESTABLISHED
17       0     0 ACCEPT     tcp  --  !lo    *       0.0.0.0/0            0.0.0.0/0            ctstate NEW tcp dpt:22
18      44  2640 ACCEPT     tcp  --  !lo    *       0.0.0.0/0            0.0.0.0/0            ctstate NEW tcp dpt:27017
19       0     0 ACCEPT     tcp  --  !lo    *       0.0.0.0/0            0.0.0.0/0            ctstate NEW tcp dpt:27018
20       0     0 ACCEPT     tcp  --  !lo    *       0.0.0.0/0            0.0.0.0/0            ctstate NEW tcp dpt:27019
21       0     0 ACCEPT     icmp --  !lo    *       0.0.0.0/0            0.0.0.0/0            icmptype 8 limit: avg 1/sec burst 5
22       0     0 ACCEPT     icmp --  !lo    *       0.0.0.0/0            0.0.0.0/0            icmptype 0 limit: avg 1/sec burst 5
23       0     0 ACCEPT     icmp --  !lo    *       0.0.0.0/0            0.0.0.0/0            icmptype 11
24       0     0 ACCEPT     icmp --  !lo    *       0.0.0.0/0            0.0.0.0/0            icmptype 3
25       8   452 LOGDROPIN  all  --  !lo    *       0.0.0.0/0            0.0.0.0/0           

Chain FORWARD (policy DROP 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy DROP 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            209.244.0.3          tcp dpt:53
2        0     0 ACCEPT     udp  --  *      !lo     0.0.0.0/0            209.244.0.3          udp dpt:53
3        0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            209.244.0.3          tcp spt:53
4        0     0 ACCEPT     udp  --  *      !lo     0.0.0.0/0            209.244.0.3          udp spt:53
5        0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            8.8.8.8              tcp dpt:53
6        0     0 ACCEPT     udp  --  *      !lo     0.0.0.0/0            8.8.8.8              udp dpt:53
7        0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            8.8.8.8              tcp spt:53
8        0     0 ACCEPT     udp  --  *      !lo     0.0.0.0/0            8.8.8.8              udp spt:53
9        0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            8.8.4.4              tcp dpt:53
10      52  3614 ACCEPT     udp  --  *      !lo     0.0.0.0/0            8.8.4.4              udp dpt:53
11       0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            8.8.4.4              tcp spt:53
12       0     0 ACCEPT     udp  --  *      !lo     0.0.0.0/0            8.8.4.4              udp spt:53
13    7286 1342K LOCALOUTPUT  all  --  *      !lo     0.0.0.0/0            0.0.0.0/0           
14       0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            tcp dpt:53
15       0     0 ACCEPT     udp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            udp dpt:53
16       0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            tcp spt:53
17       0     0 ACCEPT     udp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            udp spt:53
18      51  3795 ACCEPT     all  --  *      lo      0.0.0.0/0            0.0.0.0/0           
19    7127 1288K INVALID    tcp  --  *      !lo     0.0.0.0/0            0.0.0.0/0           
20    7127 1288K ACCEPT     all  --  *      !lo     0.0.0.0/0            0.0.0.0/0            ctstate RELATED,ESTABLISHED
21       0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            ctstate NEW tcp dpt:53
22       0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            ctstate NEW tcp dpt:80
23       0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            ctstate NEW tcp dpt:27017
24       0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            ctstate NEW tcp dpt:27018
25       0     0 ACCEPT     tcp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            ctstate NEW tcp dpt:27019
26       0     0 ACCEPT     udp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            ctstate NEW udp dpt:53
27       0     0 ACCEPT     udp  --  *      !lo     0.0.0.0/0            0.0.0.0/0            ctstate NEW udp dpt:123
28       0     0 ACCEPT     icmp --  *      !lo     0.0.0.0/0            0.0.0.0/0            icmptype 0
29       0     0 ACCEPT     icmp --  *      !lo     0.0.0.0/0            0.0.0.0/0            icmptype 8
30       0     0 ACCEPT     icmp --  *      !lo     0.0.0.0/0            0.0.0.0/0            icmptype 11
31       0     0 ACCEPT     icmp --  *      !lo     0.0.0.0/0            0.0.0.0/0            icmptype 3
32       0     0 LOGDROPOUT  all  --  *      !lo     0.0.0.0/0            0.0.0.0/0           

Chain ALLOWIN (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 ACCEPT     all  --  !lo    *       162.158.0.0/15       0.0.0.0/0           
2        0     0 ACCEPT     all  --  !lo    *       198.41.128.0/17      0.0.0.0/0           
3        0     0 ACCEPT     all  --  !lo    *       197.234.240.0/22     0.0.0.0/0           
4        0     0 ACCEPT     all  --  !lo    *       188.114.96.0/20      0.0.0.0/0           
5        0     0 ACCEPT     all  --  !lo    *       190.93.240.0/20      0.0.0.0/0           
6        0     0 ACCEPT     all  --  !lo    *       108.162.192.0/18     0.0.0.0/0           
7        0     0 ACCEPT     all  --  !lo    *       141.101.64.0/18      0.0.0.0/0           
8        0     0 ACCEPT     all  --  !lo    *       103.31.4.0/22        0.0.0.0/0           
9        0     0 ACCEPT     all  --  !lo    *       103.22.200.0/22      0.0.0.0/0           
10       0     0 ACCEPT     all  --  !lo    *       103.21.244.0/22      0.0.0.0/0           
11       0     0 ACCEPT     all  --  !lo    *       173.245.48.0/20      0.0.0.0/0           
12       0     0 ACCEPT     all  --  !lo    *       199.27.128.0/21      0.0.0.0/0           
13     213 17445 ACCEPT     all  --  !lo    *       59.189.154.164       0.0.0.0/0           

Chain ALLOWOUT (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            162.158.0.0/15      
2        0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            198.41.128.0/17     
3        0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            197.234.240.0/22    
4        0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            188.114.96.0/20     
5        0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            190.93.240.0/20     
6        0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            108.162.192.0/18    
7        0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            141.101.64.0/18     
8        0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            103.31.4.0/22       
9        0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            103.22.200.0/22     
10       0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            103.21.244.0/22     
11       0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            173.245.48.0/20     
12       0     0 ACCEPT     all  --  *      !lo     0.0.0.0/0            199.27.128.0/21     
13     159 53077 ACCEPT     all  --  *      !lo     0.0.0.0/0            59.189.154.164      

Chain DENYIN (1 references)
num   pkts bytes target     prot opt in     out     source               destination         

Chain DENYOUT (1 references)
num   pkts bytes target     prot opt in     out     source               destination         

Chain INVALID (2 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 INVDROP    all  --  *      *       0.0.0.0/0            0.0.0.0/0            ctstate INVALID
2        0     0 INVDROP    tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags: 0x3F/0x00
3        0     0 INVDROP    tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags: 0x3F/0x3F
4        0     0 INVDROP    tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags: 0x03/0x03
5        0     0 INVDROP    tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags: 0x06/0x06
6        0     0 INVDROP    tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags: 0x05/0x05
7        0     0 INVDROP    tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags: 0x11/0x01
8        0     0 INVDROP    tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags: 0x18/0x08
9        0     0 INVDROP    tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags: 0x30/0x20
10       0     0 INVDROP    tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags:! 0x17/0x02 ctstate NEW

Chain INVDROP (10 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           

Chain LOCALINPUT (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1    10491  986K ALLOWIN    all  --  !lo    *       0.0.0.0/0            0.0.0.0/0           
2    10278  968K DENYIN     all  --  !lo    *       0.0.0.0/0            0.0.0.0/0           

Chain LOCALOUTPUT (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1     7286 1342K ALLOWOUT   all  --  *      !lo     0.0.0.0/0            0.0.0.0/0           
2     7127 1288K DENYOUT    all  --  *      !lo     0.0.0.0/0            0.0.0.0/0           

Chain LOGDROPIN (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:67
2        0     0 DROP       udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:67
3        0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:68
4        0     0 DROP       udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:68
5        0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:111
6        0     0 DROP       udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:111
7        0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:113
8        0     0 DROP       udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:113
9        0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpts:135:139
10       0     0 DROP       udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpts:135:139
11       0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:445
12       0     0 DROP       udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:445
13       0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:500
14       0     0 DROP       udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:500
15       0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:513
16       0     0 DROP       udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:513
17       0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:520
18       0     0 DROP       udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:520
19       8   452 LOG        tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            limit: avg 30/min burst 5 LOG flags 0 level 4 prefix "Firewall: *TCP_IN Blocked* "
20       0     0 LOG        udp  --  *      *       0.0.0.0/0            0.0.0.0/0            limit: avg 30/min burst 5 LOG flags 0 level 4 prefix "Firewall: *UDP_IN Blocked* "
21       0     0 LOG        icmp --  *      *       0.0.0.0/0            0.0.0.0/0            limit: avg 30/min burst 5 LOG flags 0 level 4 prefix "Firewall: *ICMP_IN Blocked* "
22       8   452 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           

Chain LOGDROPOUT (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 LOG        tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcpflags: 0x17/0x02 limit: avg 30/min burst 5 LOG flags 8 level 4 prefix "Firewall: *TCP_OUT Blocked* "
2        0     0 LOG        udp  --  *      *       0.0.0.0/0            0.0.0.0/0            limit: avg 30/min burst 5 LOG flags 8 level 4 prefix "Firewall: *UDP_OUT Blocked* "
3        0     0 LOG        icmp --  *      *       0.0.0.0/0            0.0.0.0/0            limit: avg 30/min burst 5 LOG flags 8 level 4 prefix "Firewall: *ICMP_OUT Blocked* "
4        0     0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0

You are running that `namp` on a different host, aren't you? — MadHatter, Feb 18 '14 at 08:41
I've just seen a suspect line in the `iptables` output, but it's impossible to be more definitive without knowing the full output. Could you replace the `iptables -L` output above with that of `iptables -L -n -v --line-numbers`? — MadHatter, Feb 18 '14 at 10:07
Thanks, that's helpful. Finally, can you give us the IP address of the machine from which the `nmap` was performed? — MadHatter, Feb 19 '14 at 07:50
@MadHatter I believe the IP address is `59.189.154.164`. Oops I just noticed it in the iptables rules by including in `csf.allow`. — Nyxynyx, Feb 19 '14 at 09:30

score 3 · Accepted Answer · answered Feb 19 '14 at 10:38

Congratulations, under the influence of slow and patient questioning you've solved your own problem. Rule 13 in the ALLOWIN chain is allowing all traffic from the IP address of your test client (59.189.154.164), so when you started an MTA the nmap response went from filtered (ie, you can get to the port, but there's no listener, so you get a TCP reset) to open (you can get to the port, and someone's ready to talk to you).

That is a fairly complex ruleset, and many of the rules have zero packet counts and are therefore doing nothing for you. You may find that undertaking a full overhaul of your firewall rules with respect to your business requirements is a good investment of your time, before they trip you up again.

Cannot close Port 25 after installing postfix

1 Answers1