Tuesday, June 12, 2012

LinkedIn spam, exploits and Zeus: a deadly combination ?

Is this the perfect recipe for a cybercriminal ?:
  1. Hacking LinkedIn's password (and possibly user-) database.
  2. Sending an email to all obtained email addresses, which is urging you to check your LinkedIn inbox as soon as possible.
  3. A user unawarely clicking on the link.
  4. An exploit gets loaded. Malware gets dropped. Malware gets executed.
  5. User's computer is now a zombie (part of a botnet).

I would definitely say YES.

A reader of my blog contacted me today, he had received an email from LinkedIn which was looking phishy. We can verify that Step 1 is accomplished, by the simple fact that in the "To" and/or "CC" field of the email below, there are about ~100 email addresses. A quick look-up of a few of them on LinkedIn reveals the unconvenient truth...

Here's the email in question:

Reminder from LinkedIn. You got a new message !

Subjects of this email might be:
"Relationship LinkedIn Mail‏", "Communication LinkedIn Mail‏", "Link LinkedIn Mail" or "Urgent LinkedIn Mail‏". No doubt the subjects of this email will vary, and are not limited to these four.

Step 1 and step 2 of the cybercrook's scheme are already fulfilled. Now he just has to wait until someone clicks on one of the links. Which brings us to point 3.

Suppose someone clicks on the link. What will happen exactly ? This depends on the version of these programs that may be installed on your computer:
  • Adobe Reader
  • Java

In some cases, your browser will crash. In other cases, the page will just appear to sit there and nothing happens. In unfortunate cases, the exploit will begin doing its work. As said before, a mixed flavor of Adobe & Java exploits are used.

In this case, we will review the specific Adobe exploit. We will check with Process Explorer what exactly is happening:

The green highlighting indicates the spawning of a new process

What's this ? There's a process from Adobe Reader loaded under our Internet Explorer ? Which seems to spawn a .dll file ? Which in turn spawns another file .... Okay, you get the point here.

The PDF file has several embedded files, which are dropping malicious executables and executing them. After the process of spawning and dropping processes and executables, the malware will also clean-up any leftovers, including the PDF file at first:

Message from Adobe Reader it has crashed. Have a guess why

After the user clicks OK, everything looks fine. Right ? No, of course not. Ultimately, there's a malicious executable which will start every time the computer boots.

Interesting to note is, that there is also an attempt to exploit CVE-2006-0003. An exploit from 2006 nonetheless !

Step 3 and 4 have also been accomplished now. The user clicked on the link, the exploit(s) got loaded and the user is now infected. With what you may ask ? Well, let's review all the associated files:

The initial Java exploit - set.jar -
(when I first uploaded this sample a few hours before this blogpost, there were ZERO detections)

Result: 2/42
MD5: b0697a5808e77b0e8fd9f85656bd7a80
VirusTotal Report
ThreatExpert Report

I just now re-uploaded set.jar (17:47:41 UTC), it has now 6 detections. Most probably the Blackhole exploit kit is responsible for this attack. Microsoft identifies the file as
The corresponding CVE can be found here.

"I got Java patched, always", you might say. Great ! How about Adobe Reader ?
Result: 11/38
MD5: ad5c7e3e018e6aa995f0ec2c960280ab
VirusTotal Report
PDFXray Report
MWTracker Report

Thanks to PDFiD, we are able to see there's an AcroForm action and 6 embedded files. Basically, AcroForm is just another way to execute JavaScript in a PDF document. Embedded files are... files hidden in your PDF document:

PDFiD results

Here's our first dropped file - calc[1].exe
Result: 5/38
MD5: 4eead3bbf4b07bd362c74f2f3ea72dc4
VirusTotal Report
ThreatExpert Report
Anubis Report

Calc[1].exe will drop other files. Examples:

Result: 9/42
MD5: e7e25999ef52e5886979f700ed022e3d
VirusTotal Report
ThreatExpert Report
Anubis Report

Result: 10/42
MD5: fbc4bb046449fd9cef8a497941457f4f
VirusTotal Report
ThreatExpert Report
Anubis Report

The malware will try to 'phone home' or connect to the following IP addresses: - IPVoid Result - IPVoid Result

The IPs above ( in particular) are part of a known botnet.

After all 4 steps have been executed, Step 5 of the process is completed as well and the machine will be successfully part of a botnet. The Zeus botnet. For more information about Zeus, you can read upon the (limited in information, but sufficient) Wikipedia article:
Zeus (Trojan Horse)

There are also numerous articles on the Zeus botnet, the takedowns by Microsoft (whether they were successful or not, I'll leave in the middle), and many other reports.


So, what did we learn today ? If you do not know the answer to this question, please re-read the article again.

PATCH PATCH PATCH people ! Keep ALL of your software up-to-date ! This means Adobe, Java, but don't forget other software, for example VLC, Windows Media Player.... You get the picture.

This also includes installing your Windows patches, keeping your browser up-to-date as well as any plugins or add-ons you might have installed.

If possible, avoid using Adobe and/or Java. There are alternatives. An alternative for Adobe is for example Sumatra PDF. Just don't forget to patch the alternatives as well !

Finally, use an up-to-date Antivirus product to keep your machine safe should you not have done any patching. Chances are you might still be infected, but are already less likely.

If you are in a corporate or business network, take the necessary actions and include several layers of protection. This also includes informing your users to not click on everything in an email ! Applying the appropriate Security Rights on a machine can prevent you from having a whole lot of work.... and lack of sleep ;-) .

If you are interested in the files discussed in this post, contact me on Twitter:


  1. Thanks for the advice


    A friend

  2. Hello .. I have never seen a smart articles that you created. It really helped me to get back my ideas for writing. I will save this post, for I learn more

  3. "So, what did we learn today ?"

    Your lame.

    1. Maybe I am, maybe I am not. As long as everyone installs their updates, I'm happy.

  4. Great post, good analysis.

  5. Thanks all for your comments.

  6. I just got a fake LinkedIn reminder as the way exactly you described, and I accidentally clicked the link before noticing it is a scam.. :( I don't know what I should do now and was looking for someone's posting. What happened after click was "the page just appeared to sit there and nothing happened." Does it mean, my computer was not harmed?? I am using Mac OS. Thanks for your post and advice!!

    1. If you're using Mac OS, I doubt you were infected. If you got a login page but didn't fill in your credentials, you're not scammed.

      What you can do is install a free antivirus for Mac and perform a scan with it. If anything's found, delete it. Afterwards you can remove the antivirus (or keep it of course).


  7. First off I would like to say superb blog! I had a quick question in which I'd like to ask if you do not mind. I was interested to know how you center yourself and clear your thoughts prior to writing. I've had trouble clearing my mind in getting my ideas out there. I truly do enjoy writing but it just seems like the first 10 to 15 minutes tend to be lost simply just trying to figure out how to begin. Any suggestions or hints? Thanks!

    1. Thanks! I usually put on some music to help me focus ;-)

  8. Wow, this article is good, my brother is analyzing these things, so I am going to let him know.