Saturday, September 15, 2007

Log Correlation

I thought I'd talk about the importance of log correlation. For instance, you've found that someone is continually pinging your server. You want to see if your box is responding to the pings. Usually, you'll know right off, since most people know if their firewall was configured to block pings...I'm just using pings as a quick example, though. Log correlation usually consists of checking, for instance, web server logs against firewall logs, or Snort logs against firewall and web server logs. This helps you understand what suspicious activity is actually doing and if your server/workstation responded (and how it responded, if it did).

I run Snort on a server, along with a web server, which is firewalled with IPTables. I have Snort report what it sees to a MySQL database, although it does record captures to a PCAP file locally. I also run Modsecurity, an application firewall that is designed to sniff and possibly block traffic going to/from web servers, mainly Apache. So, I've a ton of logs that I can correlate: Snort, Apache, IPTables, and Modsecurity logs.

We'll pick something easy. In fact, I'll fabricate some logs by generating some false alerts. I'll use 'wget', to visit my website. Keep in mind that what you see below gives you the advantage...you know what you're doing and looking for when we soon check the logs. This won't be the case when some stranger or worm hits your firewall or web server (or any other application server).

-bash-2.05b$ wget wigglit.ath.cx/root.exe
--23:24:05-- http://wigglit.ath.cx/root.exe
=> `root.exe'
Resolving wigglit.ath.cx... 66.160.141.30
Connecting to wigglit.ath.cx|66.160.141.30|:80... connected.
HTTP request sent, awaiting response... 404 Not Found
23:24:06 ERROR 404: Not Found.

-bash-2.05b$
I used root.exe because there is an old vulnerability was was used to exploit the CodeRed worm of old. Now, let's check the web server's logs. I've tail'd my logs:

root@starchild:/var/log/apache# tail -f -n 100 access_log
12.123.12.123 - - [15/Sep/2007:23:34:35 -0400] "GET /root.exe HTTP/1.0" 404 202
12.123.12.123 - - [15/Sep/2007:23:34:35 -0400] "GET /root.exe HTTP/1.0" 404 202 "-" "Wget/1.10.2"
You see that the communcation was rejected (404 code), as the traffic was deemed forbidden by the web server. This is usually a good indication, as the server didn't respond favorably to the attack.

Now, let us check the firewall logs. We already know that the firewall allowed the traffic, since the web server responded with a 404...if the traffic was being blocked, there would be no record of the attack in the logs, because the firewall would have intercepted the traffic before it reached the web server. We're checking the firewall logs just to be sure this guy hasn't done anything else that the web server didn't see:

Sep 12 17:28:34 starchild kernel: Connection attempt (UNPRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=34557 DF PROTO=TCP SPT=46656 DPT=10083 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:28:44 starchild kernel: Connection attempt (PRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=18168 DF PROTO=TCP SPT=40091 DPT=449 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:28:44 starchild kernel: Connection attempt (UNPRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=27053 DF PROTO=TCP SPT=36295 DPT=5060 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:28:54 starchild kernel: Connection attempt (PRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=29291 DF PROTO=TCP SPT=47590 DPT=342 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:28:54 starchild kernel: Connection attempt (UNPRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=11788 DF PROTO=TCP SPT=43604 DPT=1519 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:29:04 starchild kernel: Connection attempt (PRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=17600 DF PROTO=TCP SPT=32783 DPT=577 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:29:04 starchild kernel: Connection attempt (UNPRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=51338 DF PROTO=TCP SPT=47879 DPT=18187 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:29:14 starchild kernel: Connection attempt (PRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=58520 DF PROTO=TCP SPT=41983 DPT=517 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:29:14 starchild kernel: Connection attempt (UNPRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=20255 DF PROTO=TCP SPT=53355 DPT=1986 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:29:24 starchild kernel: Connection attempt (PRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=28213 DF PROTO=TCP SPT=38543 DPT=978 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:29:24 starchild kernel: Connection attempt (UNPRIV): IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=60 TOS=0x00 PREC=0x00 TTL=56 ID=10244 DF PROTO=TCP SPT=45624 DPT=11371 WINDOW=5840 RES=0x00 SYN URGP=0
Sep 12 17:29:37 starchild kernel: ICMP-request: IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=28 TOS=0x00 PREC=0x00 TTL=42 ID=53002 PROTO=ICMP TYPE=8 CODE=0 ID=10683 SEQ=16615
Sep 15 17:38:25 starchild sshd[8455]: Accepted publickey for ron from ::ffff:12.123.12.123 port 33557 ssh2
Sep 15 23:21:08 starchild kernel: ICMP-request: IN=eth0 OUT= MAC=fe:fd:40:3e:e7:dc:00:0c:db:f5:90:00:08:00 SRC=12.123.12.123 DST=66.160.141.30 LEN=84 TOS=0x00 PREC=0x00 TTL=55 ID=40988 PROTO=ICMP TYPE=8 CODE=0 ID=614 SEQ=0

Quite a bit of stuff, huh? This looks to be a port scan! This is something that we didn't see in the Apache logs! Good thing we checked! Looks like this IP needs to be blocked with IPTables (which we won't do in this exercise).

Sadly, nothing shows in the Modsecurity logs, but we've enough information already. What about Snort? Because I've PCAP files, the search becomes a bit more involved. I'll spare the intimate details, but this is what we see:

[**] [1:1256:9] WEB-IIS CodeRed v2 root.exe access [**]
[Classification: Web Application Attack] [Priority: 1]
09/15-23:34:35.708546 0:C:DB:F5:90:0 -> FE:FD:40:3E:E7:DC type:0x800 len:0xB0
12.123.12.123:52753 -> 66.160.141.30:80 TCP TTL:56 TOS:0x0 ID:51589 IpLen:20 DgmLen:162 DF
***AP*** Seq: 0xAF32BB68 Ack: 0x3F319F7A Win: 0xFFFF TcpLen: 32
TCP Options (3) => NOP NOP TS: 288652007 1521931210
[Xref => http://www.cert.org/advisories/CA-2001-19.html]

23:34:35.708546 00:0c:db:f5:90:00 > fe:fd:40:3e:e7:dc, ethertype IPv4 (0x0800), length 176: IP (tos 0x0, ttl 56, id 51589, offset 0, flags [DF], length: 162) 12.123.12.123.52753 > 66.160.141.30.80: P [tcp sum ok] 2939337576:2939337686(110) ack 1060216698 win 65535
0x0000: fefd 403e e7dc 000c dbf5 9000 0800 4500 ..@>..........E.
0x0010: 00a2 c985 4000 3806 56c0 47b2 0aa0 42a0 ....@.8.V.G...B.
0x0020: 8d1e ce11 0050 af32 bb68 3f31 9f7a 8018 .....P.2.h?1.z..
0x0030: ffff e9c5 0000 0101 080a 1134 7ae7 5ab6 ...........4z.Z.
0x0040: d3ca 4745 5420 2f72 6f6f 742e 6578 6520 ..GET./root.exe.
0x0050: 4854 5450 2f31 2e30 0d0a 5573 6572 2d41 HTTP/1.0..User-A
0x0060: 6765 6e74 3a20 5767 6574 2f31 2e31 302e gent:.Wget/1.10.
0x0070: 320d 0a41 6363 6570 743a 202a 2f2a 0d0a 2..Accept:.*/*..
0x0080: 486f 7374 3a20 7769 6767 6c69 742e 6174 Host:.wigglit.at
0x0090: 682e 6378 0d0a 436f 6e6e 6563 7469 6f6e h.cx..Connection
0x00a0: 3a20 4b65 6570 2d41 6c69 7665 0d0a 0d0a :.Keep-Alive....

The first is the Snort alert file...this is a fast alert, with minimal detail (no packet capture). The second section is the full alert, including packet capture. It is also garbled (due to the hex code and the fact that this blog has issues with formatting) Note that my logs show no response. Apparently, my Snort install doesn't have a 404 signature. Again, the fact that we can correlate helps me when my Snort install lacks the data that I may have needed. I was able to look at the Apache logs to see the 404 when my Snort logs didn't show the return traffic.

Well, this concludes our chat about correlating existing logs. Note that any log files can be correlated. Correlation can also assist in tracking down network issues or issues with, for instance, a faulty Snort install (ahem). Although this discussion focused more on security, hopefully this helps someone understand their network or software architecture also.

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