Monday, January 11, 2010

What's Up With All The Port Scanning Using TCP/6000 As A Source Port?


What's Up With All The Port Scanning Using TCP/6000 As A Source Port?


Yeah, this is from ISC. I've been noticing this for awhile, but I thought it was just noise. Apparently, others noticed it too. Here's what I have (example snippet):

syslog:Jan 10 14:16:03 none kernel: BLOCKED: IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f
c:8b:69:08:00 SRC=221.194.45.3 DST=66.160.141.30 LEN=40 TOS=0x00 PREC=0x00 TTL=109 ID=256
PROTO=TCP SPT=6000 DPT=1521 WINDOW=16384 RES=0x00 SYN URGP=0
syslog:Jan 10 15:44:17 none kernel: BLOCKED: IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f
c:8b:69:08:00 SRC=218.240.32.166 DST=66.160.141.30 LEN=40 TOS=0x00 PREC=0x00 TTL=110 ID=25
6 PROTO=TCP SPT=6000 DPT=2967 WINDOW=16384 RES=0x00 SYN URGP=0
syslog:Jan 10 16:21:55 none kernel: BLOCKED: IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f
c:8b:69:08:00 SRC=61.182.168.30 DST=64.62.231.220 LEN=40 TOS=0x00 PREC=0x00 TTL=107 ID=256


Yeah, I've been blocking these. It's pretty easy, as I've a firewall policy that just flat-out blocks anything I don't outright allow...It's pretty hardcore. For those who think that "port 80 will always be open" (yeah, I do run a web-server), Modsecurity covers that port...but I'm deviating from the topic of this post.

No one seems to know what the offending IPs are doing, but most appear to originate from China. I'm running a tcpdump to try to gather data, but so far I don't have much (6 hours of sniffing only shows 4 hits so far).

I'm using the following tcpdump command:


tcpdump -i eth0 -Xvvnne -s 0 src port 6000 -w /tmp/dump_src_port_6000


I'll leave it running for 24 hours then check and see what I have...it might not amount to much, though.

UPDATE:

One thing I noticed right off the bat was the destination ports...they are all affiliated with MS Windows services (ports 135, 139, 1433, 2967, 1521) but also ports such as 8000, 8080 and 7212. Weird. I'll keep the sniff going for a few days (a week's worth of sniffing, maybe).

UPDATE #2:

Decided to kill the tcpdump process to see what's going on and post it here. Will start it up again before I head to bed (I doubt I'm missing much so far):

root@starchild:~# tcpdump -Xvvnes -0 -r /tmp/dump_src_port_6000
reading from file /tmp/dump_src_port_6000, link-type EN10MB (Ethernet)
20:06:55.553601 00:0c:db:fc:8b:69 > fe:fd:40:3e:e7:dc, ethertype IPv4 (0x0800), length 54: (tos 0x0, ttl 107, id 256, offset 0, flags [none], proto TCP (6), length 40) 221.195.73.68.6000 > 66.160.141.30.8000: S, cksum 0x3a87 (correct), 132448256:132448256(0) win 16384
0x0000: 4500 0028 0100 0000 6b06 580a ddc3 4944 E..(....k.X...ID
0x0010: 42a0 8d1e 1770 1f40 07e5 0000 0000 0000 B....p.@........
0x0020: 5002 4000 3a87 0000 P.@.:...
21:06:16.773790 00:0c:db:fc:8b:69 > fe:fd:40:3e:e7:dc, ethertype IPv4 (0x0800), length 54: (tos 0x0, ttl 109, id 256, offset 0, flags [none], proto TCP (6), length 40) 121.101.212.38.6000 > 66.160.141.30.1433: S, cksum 0xca79 (correct), 1796538368:1796538368(0) win 16384
0x0000: 4500 0028 0100 0000 6d06 2f86 7965 d426 E..(....m./.ye.&
0x0010: 42a0 8d1e 1770 0599 6b15 0000 0000 0000 B....p..k.......
0x0020: 5002 4000 ca79 0000 P.@..y..
21:36:31.664717 00:0c:db:fc:8b:69 > fe:fd:40:3e:e7:dc, ethertype IPv4 (0x0800), length 54: (tos 0x0, ttl 110, id 256, offset 0, flags [none], proto TCP (6), length 40) 60.13.26.66.6000 > 64.62.231.220.1433: S, cksum 0xd34d (correct), 19005440:19005440(0) win 16384
0x0000: 4500 0028 0100 0000 6e06 cd66 3c0d 1a42 E..(....n..f<..B
0x0010: 403e e7dc 1770 0599 0122 0000 0000 0000 @>...p..."......
0x0020: 5002 4000 d34d 0000 P.@..M..
22:00:21.259640 00:0c:db:fc:8b:69 > fe:fd:40:3e:e7:dc, ethertype IPv4 (0x0800), length 54: (tos 0x0, ttl 106, id 256, offset 0, flags [none], proto TCP (6), length 40) 222.45.112.219.6000 > 66.160.141.30.135: S, cksum 0xe3c1 (correct), 1432485888:1432485888(0) win 16384
0x0000: 4500 0028 0100 0000 6a06 3109 de2d 70db E..(....j.1..-p.
0x0010: 42a0 8d1e 1770 0087 5562 0000 0000 0000 B....p..Ub......
0x0020: 5002 4000 e3c1 0000 P.@.....


I'm not seeing much but my FW is definitely not helping things, either (killing the connections, which is why you can only see syn packets). Well, anyone else want to guess what's going on?
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