Ransomware gets the big headlines, because of the enormous blackmail demands that typically arrive at the end of ransomware attacks.
Indeed, the word “ransom” only expresses half the drama these days, because modern ransomware attacks usually involve the crooks making copies of all your data first before scrambling it.
The crooks then demand a combination payout, part ransom and part hush-money.
You’re not only paying to get the local copies of your data unscrambled, but also paying for a promise from the crooks that they’ll delete all the data they just stole instead of releasing it to the public.
But what about the very start of a ransomware attack?
Technically, that’s often a lot more interesting – and often more important, too, given that many ransomware attacks are merely the final blow to your network at the end of what may well have been an extended attack lasting days, weeks or even months.
Given the danger that arises as soon as the crooks sneak into your network, it’s as important to learn how malware gets delivered in the first place as it is to know what happens to your files when ransomware finally scrambles them.
With this in mind, SophosLabs has just published an intriguing report on a malware delivery ecosystem dubbed Gootloader.
You may have heard reference to Gootkit, a name given to the malware family of which Gootloader forms a part, because it’s been around for several years already.
But SophosLabs decided to give the initial delivery mechanism a name of its own and study it in its own right:
The Gootkit malware family has been around more than half a decade – a mature Trojan with functionality centered around banking credential theft. In recent years, almost as much effort has gone into improvement of its delivery method as has gone into the NodeJS-based malware itself.
In the past, Sophos and other security experts have bundled the discussion of the malware itself with analysis of the delivery mechanism, but as this method has been adopted to deliver a wider range of malicious code, we assert that this mechanism deserves scrutiny (and its own name), distinct from its payload, which is why we’ve decided to call it Gootloader.
The report goes into the sort of detail that is well worth knowing if you’re interested in how modern malware embeds and extends itself inside a network, including a discussion of so-called “fileless” attacks.
The term fileless attack is a bit of a misnomer, because “fileless” malware often involves at least one physical file to get the malware started, and may also rely on various intermediate files along the way. But fileless malware is entirely unlike regular software in the way it operates. Well-behaved software typically installs its executable code into a self-contained directory on your hard disk, uses the registry to save its configuration settings, and relies on the operating system to load its various software modules into memory and keep them under control. Fileless malware flouts these conventions (ironically, it often uses the registry as a sneaky place to store obfuscated versions of its executable code), loading its malware code directly into memory in order to bypass the regular tools that sysadmins use to monitor the system for unexpected and unwanted processes.
Search treachery
Even if you aren’t an assembly language expert or a malware analyst, the SophosLabs paper is well worth reading for its description of how the Gootloader criminals lure well-meaning users into installing the Gootloader malware in the first place.
Simply put, the crooks game Google’s search engine, tricking Google into treating hacked websites as trustworthy sources, and presenting innocent users with apparently “perfect matches” to their search queries.
(As far as we can tell, this gang has focused its effort on poisoning Google searches, but the tricks below could be used against other search engines, too.)
The report explains the process in detail, but we’ll summarise it here:
- The crooks hack into hundreds of innocent web servers and implant artificially generated content containing phrases that search engines are likely to associate with expertise in a specific field. Examples include real estate, employment law, import/export regulations, company partnerships, and more.
- From time to time, the crooks get lucky and one or their hacked sites turns up as a top hit on Google, typically thanks to a very specific search term entered by an innocent user. There’s a good chance that the user will click the Google link that shows up, because the search hit looks like a natural result, given that it’s not a paid ad or a sponsored link.
- If the user clicks through to the hacked server, the crooks recognise that the click came via a Google search by using the
Referer:header (yes, the header name was mis-spelled in the original specification) in the web request. The server deliberately concots a fraudulent web page that looks like a message board on which someone else recently asked the same question. - The bogus message board page includes an exact duplicate of the question that the new visitor just asked, together with what looks like a reply from a site administrator recommending a download link that answers the question. To make the page look even more convincing, there’s then a further reply, apparently from the original questioner, thanking the administrator for their prompt and helpful answer.
SophosLabs has encountered Gootloader’s fake message board pages in a variety of different languages, including English, German, French and Korean, with different campaigns targeted at different regions.
Here’s an English-language example from the paper, where the unfortunate visitor had searched for the very specific phrase intercompany settlement agreement (chart) alberta:
A veneer of believability
As you can see, the search term doesn’t fit grammatically into the boilerplate text used by the Gootloader crooks, but it looks realistic enough at a glance.
The vote of thanks from the “happy user”, together with the fact that the datestamps are recent, gives the content a veneer of believability..
The name of the web page that’s presented, the download link that shows up, and the name of the file offered for download, are all constructed from the search phrase in order to make the fake page seem like a perfect fit for the query.
The deeply devious part of this, of course, is that the crooks don’t need to guess in advance what search text a hapless visitor is going to type into Google.
All the crooks need is for Google to think that one of the hacked-and-poisoned websites is a good enough match for the search term entered.
Of course, when the unexpecting visitor arrives at the booby-trapped site, the crooks tailor the response on the fly to make it look as though Google found an exact hit for their query, not merely a near-enough match.
Note that although the hacked site displays the malicious download link, the link itself points off to a different download server.
We’re assuming that the crooks are using this two-stage approach so that the Gootloader malware files themselves don’t show up on the hacked site, which helps the hacked site to keep a clean reputation for a lot longer than it otherwise might.
What to do?
- Stop. Think. Connect. This search poisoning trick works because the website you visit seems to fit your search perfectly, which feels like too much of a coincidence for a crook to have anticpated it in advance. But if you look at the imposter page carefully, you should spot that it’s a carefully constructed set-up designed to look like a lucky coincidence. Remember the cybersecurity adage, “If it looks too good to be true, it IS too good to be true!”
- Use an anti-virus with a built-in web filter. A search poisoning subterfuge like this gives your web filter not one but three chances to spot the treachery. It will prevent this attack proactively if it blocks the first click to the hacked site, or the second click to the download URL, or the final download, even before the malware reaches your computer in a dangerous form.
- Use an anti-virus with in-memory exploit protection features. Don’t rely on file-based scaning and detection alone. Augment your protection with behaviour monitoring tools that can detect programs that start out harmless but turn malicious in memory after running, apparently inncocently, for a while.
- Tell Windows to show file extensions. The Gootloader samples described in the report arrive as a JavaScript program file compressed inside a ZIP file. With file extensions turned off, JavaScript programs lack the telltale marker
.JSat the end of the filename, and they show up with an icon that looks like a scroll of parchment. This makes it easy to misidentify them as harmless text files.
To tell Windows to show file extensions, go to File Explorer, click on the View item in the menu bar and then turn on the option File name extensions. If the Explorer window is narrow you may need to open the Show/hide tab first.
