Immutable Security

Sometimes security measures can be completely correct and at the same time, completely useless. Such is the case when viewing the logs of a user added to the local Administrators group on a Windows 2003 server.

Here is what an OSSEC syslog-formatted alert looks like in this case:

Mar 3 11:04:39 hostname ossec: Alert Level: 8; Rule: 18114 – Group account changed.; Location: (hostname) 172.16.0.1->WinEvtLog; user: username; WinEvtLog: Security: AUDIT_SUCCESS(636): Security: username: HOSTNAME: HOSTNAME: Security Enabled Local Group Member Added: Member Name: – Member ID: %{S-1-5-21-2533786115-122353884-3837542848-1670} Target Account Name: Administrators Target Domain: Builtin Target Account ID: %{S-1-5-32-544} Caller User Name: username Caller Domain: DOMAIN Caller Logon ID: (0×0,0×11529569) Privileges: -

Pop quiz: Tell me who was added to the Administrators group. If your answer is S-1-5-21-2533786115-122353884-3837542848-1670, then you are correct. Now tell me who that really is. Is it Bob from accounting or is it a l33t hacker? What will you tell your auditors? Without the Member Name, how can you know?

By now you may be thinking, “this is clearly an OSSEC bug.” That’s what I thought, too. But as it turns out, Snare exhibits the exact same behavior. And so does another commercial log aggregation tool I have used. So what’s going on here?

When viewing this alert in the Windows Event Viewer, the Member Name also displays the dash (-), but resolves the Member ID at the application layer (if it can). If there is no corresponding user, the SID is displayed. The Member Name is not in the raw log at all.

On one hand, this could be seen as correct behavior. After all, the administrator “Bob” from two years ago may not be the same administrator named Bob who was just hired last week. From a log integrity perspective, presenting the unique SID, which is never duplicated, is correct.

On the other hand, having the Member Name is entirely useful and relevant from the practicality and usability perspective. Who the heck is S-1-7-23-3394466182-97151736-2635146241-1084? Should I be concerned? I don’t know.

Just when you thought this was starting to make sense, a domain controller exhibits different behavior. In that case, the Member Name is populated. If it is a domain member or a stand-alone system, it is not.

To me, the correct behavior seems to be to write both the Member Name and the Member ID to the raw log. That way, the log analyst can clearly see that these were different Bobs. By correlating the timeline of the logs with other activities, we can put the pieces of the puzzle together.

Why did Microsoft not do this? I’d love to know. If you know, please enlighten us in the comments.

Here’s a little secret that the sales guys of the million-dollar SIEMs are probably going to gloss over. Most of them do not offer a way to encrypt logs in transit end-to-end. Worse, many of them use downright silly methods to collect logs on common operating systems, such as installing an FTP client on every host and sending them along as a big batch every so often.

For some reason, this is seen as acceptable since it’s usually on the internal network. At the same time, we give mean looks to anyone who even mentions the use of a clear-text protocol like telnet.

Here’s another little secret: many of the big SIEM vendors use syslog-ng as the log daemon on their appliances. It’s reliable and secure and generally works very well.

What if there was a way to add encrypted log transit to the expensive SIEM, or to the other log management solution you already have in place? What if you can’t use or don’t need the full functionality of a log analysis solution like OSSEC, but would like the ability to use encrypted log transport? Read on, my friend, because I’m going to show you exactly how to do that, and it can be done in just a few minutes.

1. Install OSSEC in server mode on the existing syslog server from the vendor. I won’t go into detail here on how to install OSSEC, as it’s well documented elsewhere. These systems are generally just minimal Linux installations, so if you are lacking a compiler then you may need to install it on a like system and move OSSEC over. If your vendor won’t let you do this, ask them why you are paying them gobs of money without even the basic functionality of encrypted log transit!
2. Install OSSEC agents on the hosts you want to collect logs from. Configure the agents to collect the logs you are interested in and add them to the manager. Don’t forget to restart the OSSEC manager after adding the agents.
3. Add the following lines to /opt/syslog-ng/etc/syslog-ng.conf under the “source s_local” section:
   # Read OSSEC queue
   unix-dgram(”/var/ossec/queue/ossec/queue”);
4. Edit /var/ossec/etc/ossec-control and modify the two variables which are responsible for starting the OSSEC daemons. After modification, they should look like this:
   DAEMONS=”ossec-remoted”
   SDAEMONS=”ossec-remoted”
5. Finally, stop both syslog-ng and OSSEC. Start syslog-ng first, then start OSSEC.

The reason this works is due to the way OSSEC is designed. In fine Unix tradition, OSSEC separates the tasks into individual daemons that do only one job and do it well. In this case, ossec-remoted is writing to a Unix socket that syslog-ng is reading from in real-time. OSSEC is simply handing off the message to the local syslog daemon, at which point the message continues on its way as it normally would.

I used to use Snare, Zebedee and OSSEC for secure log delivery and file integrity. Now, it can all be handled with one open-source agent, already designed for secure and reliable log delivery.

There is a downside, which is primarily due to me not taking this to the next level and looking into the issue. In this configuration, you will not receive a notification if the OSSEC agent disconnects, since there is nothing to act on the absence of the heartbeat OSSEC sends. I’m pretty sure that can be solved by taking it up a notch and including one or two more daemons, combined with a stripped down decoder and rules file.

So the next time your expensive SIEM vendor tells you there’s no way to encrypt the logs in transit, tell them you can set it up in under an hour. Then send them a bill for your time.