This Phishing Campaign Spoofed a CDC Warning to Deliver the Latest GandCrab Ransomware

CISO Summary

Cofense IntelligenceTM reports that threat actors have spoofed a CDC email—this one warns of a flu epidemic—to deliver an updated variant of GandCrab ransomware. Besides competing for a new low in predatory cyber-crime, the phishing campaign follows the public release of a decryptor tool for infections of recent GandCrab versions, through version 5.1. The fake CDC email contained version 5.2, which renders the decryptor tool ineffective.

Though ransomware has dropped off over the past year, the authors of GandCrab are still pushing out frequent, powerful updates.  GandCrab is the last of the infamous “ransomware as a service” threats. The extent to which its creators make upgrades, parrying and thrusting with security researchers, shows it’s still a very real weapon for revenue-hungry criminals.

Full Details

Recent updates to GandCrab Ransomware demonstrate that its operators remain committed to the malware’s effectiveness and are prepared to make urgent changes to overcome disruptions. Shortly after a coordinated public release of a decryptor tool for infections of GandCrab versions 5.0.4 through 5.1, Cofense Intelligence observed GandCrab v5.2 campaigns that rendered the tool ineffective.  In a recent phishing email delivering GandCrab, a fabricated flu epidemic alert from the Center for Disease Control (CDC) was crafted to terrify recipients into opening an attached document. Far from receiving potentially life-saving instructions, the Office document was laden with macros, coded to download and execute a copy of—you guessed it— GandCrab v5.2.

Natural disasters, global geopolitical events, and pandemics are perfect narrative drivers for threat actors seemingly devoid of conscience, tact, or taste. Self-preservation is a human imperative, and such narratives that evoke fear and urgency are potentially more effective than those exploiting greed, empathy, or curiosity, other typical phishing narratives.

Coughs and Splutters

Despite leveraging a powerful concept, the execution of the observed campaign leaves much to be desired. Figure 1 shows the body of a typical message from this campaign.

Figure 1: a typical message observed during this campaign

Ostensibly, the message is well-structured, somewhat professional and believable. However, a closer read would note the grammatical errors and unusual statements. The content of the attached document continues this trend, with such preposterously low effort as compared to the effort put into the phishing email. Figure 2 shows the content of the document, displayed to the user while the macros are busy downloading and executing GandCrab.

Figure 2: the content of the document, typically deployed as a decoy.

In scenarios that leverage weaponized documents as the attack vector, threat actors often disseminate believable content to distract the user while whatever required background processes run.

Where’s Trik?

A noticeable deviation from the recent standard GandCrab protocol is the absence of an intermediate loader. Since Feb 2019, all phishing campaigns that ultimately served GandCrab did so via Trik, a spambot with pretentions of data-stealer. Certainly not a wholly unique occurrence, it does reverse a trend that had been forming.

Despite ransomware becoming less and less lucrative, the actors behind GandCrab continue to push out extremely frequent and pertinent updates. On February 19th 2019, Bitdefender released a decryption tool for GandCrab V5.1. Later that same day, it came to light v5.2 – a version for which no available decryption utility would work – had already been released, seemingly in direct response to the decryption utility.

GandCrab is the last great bastion of the ransomware-as-a-service world. Its frequent updates, active engagement with security researchers, and novel abuse of vulnerabilities and weaknesses makes it a very real, and potentially very devastating, threat. By appealing to fear and self-preservation, this campaign highlights to what lengths threat actors will go to generate revenue.

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Flu pandemic warning.doc        054607600b11e09fa74aa39c790357d6

perdaliche.exe                         b47b281a8d1f227d6a7f48f73192e7ed






All third-party trademarks referenced by Cofense whether in logo form, name form or product form, or otherwise, remain the property of their respective holders, and use of these trademarks in no way indicates any relationship between Cofense and the holders of the trademarks.


The Malware Holiday Ends—Welcome Back Geodo and Chanitor

CISO Summary

Even cybercriminals knock off for the holidays. Then in January, it’s back to work. We all have bills to pay.

This past holiday season, including the Russian Orthodox Christmas which fell on January 7, threat actors cooled their heels and malware campaigns dipped. But with the holidays over, threat actors are back in action. Chanitor malware campaigns are spiking, at even higher levels than a year ago, and Geodo/Emotet campaigns have been surging too.

In 2018, Cheap and Easy Malware Flooded Corporate Inboxes

CISO Summary

Sometimes it’s the simple things that make life hard. In 2018, over 2/3 of unique malware campaigns Cofense IntelligenceTM observed were simple, inexpensive “stealers” or remote access trojans (RATs). With exceptionally low barrier-to-entry—an email account or website can handle distribution and communication—these malware types make data theft a viable career choice for threat actors without the skills to use more advanced varieties.

A Staggering Amount of Stolen Data is Heading to Zoho Domains

After last month’s brief domain suspension of Zoho—which resulted from an insufficient response to reported phishing abuse— Cofense Intelligence™ has uncovered Zoho’s connection to an extremely high number of keylogger phishing campaigns designed to harvest data from infected machines. Of all Keyloggers analysed by Cofense, 40% used a or email address to exfiltrate data from victim machines.

Recent Geodo Malware Campaigns Feature Heavily Obfuscated Macros

Part 3 of 3

As we mentioned in our previous overview of Geodo, the documents used to deliver Geodo are all quite similar. Each document comes weaponised with a hostile macro. The macros are always heavily obfuscated, with junk functions and string substitutions prevalent throughout the code. The obfuscation uses three languages or dialects as part of the obfuscation process: Visual Basic, PowerShell, and Batch.

Twin Trouble: Geodo Malware URL-Based Campaigns Use Two URL Classes

Part 2 of 3

As discussed in our prior blog post, URL-based campaigns – that is, campaigns that deliver messages which contain URLs to download weaponised Office documents – are by far the most prevalent payload mechanism employed by Geodo. Indeed, analysis of ~612K messages shows just 7300 have attachments; a trifling 1.2% of the total. The structure of the URLs falls into two distinct classes. Cofense Intelligence™ analysed a corpus of 90,000 URLs and identified 165 unique URL paths. There are two distinct classes of URLs employed by Geodo. A detailed breakdown of these URL structures follows. 

Into a Dark Realm: The Shifting Ways of Geodo Malware

The Geodo malware is a banking trojan that presents significant challenges. For starters, it conducts financial theft on a vast scale and enables other financially driven trojans. Also known as Emotet, Geodo has a rich history, with five distinct variants, three of which are currently active according to Feodo Tracker. Geodo’s lineage is incredibly convoluted and intertwined with malware such as Cridex as well as the later iterations known as Dridex.

This blog is the first of a CofenseTM three-part series on Geodo. Our analysis of Geodo focuses not on code analysis, rather on observed behaviours, infrastructure choices and proliferation. We note there has been an upward trend of education and government-based mail account credentials being compromised and used to further distribute Geodo. Further, we investigate message content and its focus on financial themes and narratives.

Future blogs will dive into the technical details of the URL structures prevalent in Geodo campaigns and will feature an in-depth analysis and deobfuscation techniques for the multi-layered macro code found within these documents.


Geodo has been steadily building momentum during 2018; after a quiet first quarter, campaigns involving Geodo have increased significantly both in frequency and density. Cofense Intelligence™ is seeing more consecutive days of campaigns, as well as more campaigns per day. Chart 1 details the year-to-date trends of Geodo as tracked by Cofense Intelligence.

Chart 1: The yearly trends of campaigns involving Geodo or its derivatives.

 A very recent change in Geodo’s behavior has seen the banking Trojan move away from its stealer roots and move towards the loader space. Recent campaigns have seen Geodo conditionally deliver either TrickBot or Zeus Panda, both of which would be considered competitors to Geodo’s banking functionality. The actors behind Geodo had been testing the water of competitor delivery as far back as March 26th, 2018, where a campaign delivering Geodo via weaponised Microsoft Office documents led to a further infection of Zeus Panda (See TID 11199). The authors of banking trojans are continually pushed to combat and overcome evolving financial security measures, such as Multi-Factor Authentication (MFA) and software-based security solutions. This arms-race could well be a motivator for the actors behind Geodo’s distribution having moved to the long-term revenue strategy of leasing out their botnet as a loader platform.

Geodo overwhelmingly favours an infection chain of:

Malicious URL → Downloaded Office Document → Macro → Geodo.

Geodo heavily favours both package delivery notices and financial institution-themed campaigns. Figure 1 is a world cloud based upon all Geodo campaigns observed by Cofense IntelligenceTM since tracking began. Figure 2 details campaigns observed strictly in 2018.

Figure 1: A word cloud generated from subject lines captured since tracking began.

Figure 2: Geodo campaign subject lines identified via tracking and botnet injection

Over time, Geodo has expanded from a propensity towards delivery-themed campaigns (spoofing companies like DHL, FedEx, and UPS), to Banking and financial narratives. However, this new focus does not preclude the tendency to spoof legitimate institutions, such as Bank of America and Chase bank. Chart 2 details the breakdown of campaigns throughout 2018, by [imitated] brand.

Chart 2: A breakdown of brands being spoofed by Geodo in 2018. Note: Generic Malware Threat is assigned to campaigns that do not imitate a legitimate entity or organisation. Note: the redacted entry is a large banking entity.


Geodo is a self-perpetuating bot. Once running on a machine, it actively begins to spam copies of itself to a victim list retrieved during one of its many check-ins to a plethora of C2 nodes, as well as addresses harvested directly from local contact lists. Typically, the messages sent by an infected host will contain either a URL from which a potential victim can download a weaponised Office document, or it will have that type of document attached directly to the message.

Message Structure

Geodo uses a subtle marker to track which bots are delivering messages on behalf of the actor(s) behind the campaigns. The Message-ID field of each message contains an identifier which can potentially be used to identify which bot sent a particular message. At this moment, the structure of the message ID is:


<20 numeric characters>.<16 hex characters>@<recipient domain>

A more literal example could be:

The identifier is a unique number assigned to each message as it is generated and sent by a bot. We have observed the identifier change as a bot progresses through its assigned list of recipients, then subsequent campaigns, as the bot becomes active again. Despite not changing linearly or sequentially, the general trend of these identifiers has seen the character count increase from 15 to 19-20.

There are several key pieces of data that can guide us toward some likely reasons for this behavior:

  1. The identifier ranges are not unique to each bot – multiple bots can have overlap within the same range.
  2. Identifiers do not always increment sequentially. This is true across multiple bots.
  3. Since tracking began, the identifier size has risen consistently from 15 bytes, up to 19-20 bytes.
  4. There are never any identifier collisions, even across different infections.

These four points lend credence to the supposition that these identifiers not only serve the functional purpose of a Message-ID (to act as a globally unique identifier of a message), but also allow the actors behind Geodo to track which bot is sending which message. By seeding recipient lists with attacker-controlled email addresses, it is possible to programmatically identify which bots are not sending messages as expected, and could be compromised, offline or otherwise in an undesirable state. With this information, attackers may be able to figure out which bots are legitimate infections, and which are researcher-controlled, thus giving them the capability to selectively send bogus templates or data to these compromised nodes.

The second part of the Message-ID structure is a 16 character hex string. As with the identifier, each hex string is unique to the message, meaning it is most likely a hash of some kind.

The final part of the Message-ID is simply the recipient’s own domain.


URL-based campaigns – that is, campaigns that deliver messages which contain URLs to download weaponised Office documents – are by far the most prevalent payload mechanism employed by Geodo. Indeed, analysis of ~612K messages shows just 7300 have attachments; a trifling 1.2% of the total. The structure of the URLs falls into two distinct classes. Cofense Intelligence analysed a corpus of 90,000 URLs and identified 165 unique URL paths.

There are two distinct classes of URLs employed by Geodo. A detailed breakdown of these URL structures will be discussed in an upcoming blog.

Chart 3: A breakdown of the top 10 URL tokens extracted from the 1000 most recently observed URLs.

A typical email from a URL-based campaign can be seen in Figure 3. Heavily contrasting TrickBot’s focus on social engineering, Geodo campaigns are fairly often lacking in any genuine attempt at brand imitation, beyond merely stating a name and perhaps a disclaimer.

Figure 3: An example of a Geodo email delivering a URL.

Figure 4 details the type of network activity that might occur, should a victim click on a link in one of these messages. When clicked, the user’s default browser is opened, and the download occurs directly. In the case of Google Chrome, the user typically will receive multiple warnings that the file being downloaded is hostile and requires multiple steps to allow the download to finish. Figures 5 and 6 details this process.

Figure 4: A Wireshark capture of the HTTP conversation after a live link is clicked.

Figure 5: A warning bar at the base of the Google Chrome browser warns the user the file is dangerous.

Figure 6: The user is required to click “Keep Dangerous File” followed by “Keep anyway” before Chrome will release the quarantined file.

Despite Chrome doing an admirable job of identifying some of the malicious documents, the permutations employed by the Geodo actors allows a significant number of documents to pass by unnoticed. Further stymying the malicious actors’ efforts: the downloaded documents are tagged with a “MotW” — or “Mark of the Web” – which, as seen in Figure 7, can potentially require further engagement by the recipient to finally get the file opened. A ZoneID of 3 indicates that the file is from the Internet Zone.

Figure 7: The downloaded documents are tagged with a Mark of the Web.


Although comparatively rare, Geodo campaigns occasionally deliver attachments instead of malicious URLs, but the narratives and themes used for these campaigns do not noticeably differ. Figure 8 shows an example of a message from an attachment-based campaign. This campaign used a generic theme with no identifiable company or entity being imitated.

Figure 8: An example message from an attachment-based, Geodo campaign.

Digging into a corpus of ~7500 filenames (examples of which are presented in Table 1) shows a very distinct set of naming conventions. These can mostly be described by a regular expression, with a few caveats.

Table 1: Example filenames used during very recent Geodo campaigns.

The naming structure bears very close resemblance to certain segments of URLs, described in detail in the next blog in this series. Although drawing any conclusions from this would be fallacious, it could potentially be used to predict the structure of a successor campaign.

Weaponised Office Documents

Regardless of which vehicle was used as the transport medium, the documents are invariably, intuitively similar. Each document comes weaponised with a hostile macro. The macros are always heavily obfuscated, with junk functions and string substitutions prevalent throughout the code. The obfuscation uses three languages or dialects as part of the obfuscation process: Visual Basic, PowerShell, and Batch.

An upcoming blog will provide an in-depth analysis of the deobfuscation techniques for the multi-layered macro code found within these documents.


The general behaviour of Geodo has been covered in extreme depth both by Cofense and the greater InfoSec community, so we will not rehash those analyses here. Rather, we will focus on Geodo’s ubiquitous spamming capabilities and the methods it uses to facilitate such behaviour.

Geodo is a modular trojan, which means most of its functionality is abstracted away from the core code and placed in external files that can be selectively imported and executed. One such example is the “spam” module. This module facilitates not only the distribution of spam, but also the validation of stolen credentials.

Geodo has two primary means of obtaining credentials. One way is retrieving a list along with the spam module. The other harvests accounts from the local machine, using a variety of external utilities. When new accounts are discovered, their credentials are validated before any attempt is made to communicate them. Figure 9 shows the credential validation phase of the spam process.

Figure 9: The credential validation phase. Each set of credentials is validated before it is used to send spam messages.

If a set of credentials is validated, spam messaging begins in earnest. Figures 10 and 11 show a Wireshark capture of a bot testing credentials before delivering messages to multiple recipients. These recipients are chosen from a large pool of email addresses containing hundreds of thousands, perhaps millions of addresses. It is unlikely that any bot ever receives a complete list of recipient addresses, meaning the sheer number available to Geodo is staggering.

Figure 10: A Wireshark capture of Geodo testing a set of credentials, before using them to authenticate and begin sending the current template.

Figure 11: Geodo iterates through its recipient list and continues to send phishing messages, using the same session.

Geodo is in constant contact with its C2 hosts. Geodo comes hardcoded with anywhere from 30-45 IP addresses, each pointing to a compromised (or, in some cases, outright malicious) web server. Most of these use Nginx as a reverse proxy to forward connections onto the actual command and control hosts. Figure 12 shows an approximate interpretation of this infrastructure.

Figure 12: An approximate representation of the Geodo infrastructure. It should be noted that there’s a high chance the proxies are tiered or layered; this representation defines a single-layer proxy configuration.

As part of its communications with the C2 infrastructure, Geodo is constantly polling for updates, commands, or instructions. Threat actors behind Geodo frequently deploy new email templates, updated C2 lists, and other module specific instructions or data. In the case of the spam module, we have actively observed Geodo launching spam campaigns against yet unseen victims in addition to new, stolen credentials. This type of information exchange is very unlikely to be unidirectional. To keep the recipient and credential lists fresh and relevant, Geodo must communicate dead recipients, bad credentials, or bad hosts.  Geodo has also been directly observed updating passwords for usernames as they become available. This type of information exchange allows the Geodo actors to automatically adjust their lists in as near real-time as is feasible, but it does open the botnet up to vulnerabilities.

It is plausible that researchers could poison the entire botnet from just a few hosts. Researchers could monitor the credentials being used by each bot, then create an account on the infected device that matches the username but contains a bad password. When the bot attempts to verify the authenticity of the new password and connects to a researcher-controlled SMTP host to accomplish this, the researcher’s host responds that authentication has been successful. Geodo will not only go ahead and begin spamming out phishing emails (as demonstrated in Figures 10 and 11), but it will also report the updated credentials to the C2 infrastructure. These bad credentials will propagate throughout the botnet and, potentially, cause large scale interruptions to its activity.

At the time of analysis, Cofense has tracked ~31,000 credential sets in a very short time. Charts 4 through 6 show multiple interpretations and permutations of this data.

Chart 4: Compromised credentials by Top-Level-Domain (TLD).

Chart 5: Compromised Credentials by Second-Level-Domain (SLD).

Chart 6: Compromised credentials by domain.

Beyond being interesting purely as data points, tracking the domains to which the compromised credentials belong allows us to actively see where outbreaks are succeeding. Spikes for certain TLDs (such as .edu) might indicate the actors are targeting students and educators. A rise in occurrences of SLDs (Second-Level Domains) could indicate the targeting of UK-based government agencies.

For many reasons, Geodo is a hugely problematic trojan. Its primary distribution method contributes an enormous amount of daily spam and phishing volumes. Not only does it engage in financial theft, but also enables additional finance-driven trojans. It can spread laterally across a network and steal credentials from a large array of software – further perpetuating the spam problem. Staying on top of these threats means employing timely, pertinent, and high-fidelity training to help users become familiar with this prolific threat. Security in depth means the ability to know not only “what”, but also “who.”

For a look behind and a look ahead at major malware trends, view the 2018 Cofense Malware Review.


All third-party trademarks referenced by Cofense whether in logo form, name form or product form, or otherwise, remain the property of their respective holders, and use of these trademarks in no way indicates any relationship between Cofense and the holders of the trademarks.

July Malware Review: Geodo and TrickBot Flex Their Muscles

The Cofense IntelligenceTM team has wrapped up our analysis of mid-summer malware. To get this summary started, let’s look at a couple of charts. 

Chart 1: Top 5 malware delivery methods, by campaign, identified in July

Chart 2: Top 5 malware families, by campaign, identified in July

In our Strategic Analysis released on Thursday, 26th July, it was noted that Geodo and TrickBot had been unusually active in recent weeks, following a lull in June and into early July. Charts 3 and 4 expand upon this observation via side-by-side comparisons and year-to-date trends.

Prior to July, both TrickBot and Geodo tended to have peaks of activity, followed by periods of inactivity, after which the malware underwent a code update. Although still true of TrickBot, Geodo has been incessant throughout July. Chart 2 shows that TrickBot is the 5th most prevalent malware family, and Geodo does not appear at all. This phenomenon occurs due to the way different actors distribute their malware. Geodo and TrickBot, for example, are distributed in campaigns comprising hundreds of thousands or even millions of messages. These campaigns tend to be long, and go through several permutations during the distribution, but are certainly all the same campaign. In comparison, other campaigns that use off-the-shelf type malware, such as Loki, Pony, and jRAT, are distributed in much, much lower volumes, but with significantly higher variance in the message structure and IoCs. Such variance defines the campaigns.

Chart 3: A side-by-side comparison of Geodo (black) and TrickBot (green) over 2018 YTD

Chart 4: July’s Geodo (black) and TrickBot (green) campaigns

Moving into August, Geodo is still extremely active, with persistent, daily campaigns, whereas TrickBot has been comparatively silent since the 31st of July. As noted above, this behavior is likely part of TrickBot’s normal cycle, and will certainly reappear extremely soon, possibly with a new update. Cofense Intelligence, being tapped directly into the Geodo botnet, has been able to compile a database of the most frequently used terms in Geodo campaign subjects. Table 1 details the top 10 subject lines across 7 days’ worth of campaigns, spanning hundreds of thousands of messages. Although appearing to end somewhat abruptly, the subject lines have been cleansed of any potential PII, because the actors behind these campaigns typically incorporate the [purported] name of the recipient into the subject line.

Table 1: Top 10 Geodo subject lines for August. The Occurrences column reflects a representative sample of the whole collection

Typically, Geodo has been seen using mainly payment notification narratives. But in July, there was a vastly more diverse range of finance-driven subject lines, as detailed in the word cloud in Figure 1.

Figure 1: A word cloud detailing the most frequently used Geodo campaign subject lines from July 1st to August 7th, 2018

Despite being an established, modular banker with a herculean pedigree, Geodo is finding its feet as a loader and distributor of other malware. Sporting several distinct iterations of the family, Geodo is mature code backed by sophisticated threat actors, themselves supported by a robust delivery infrastructure. It is prolific and, potentially, the greatest current threat offered by any mainstream malware family. Despite the volume-to-campaign ratio, as mentioned above, being heavily skewed towards volume, their sheer magnitude, and the virulence of the malware, leave no doubt it is a force with which to be reckoned.

Keep an eye on this blog for an in-depth examination of Geodo and its infrastructure. For a look back and a look ahead at major malware trends, see the 2018 Cofense™ Malware Review.


All third-party trademarks referenced by Cofense whether in logo form, name form or product form, or otherwise, remain the property of their respective holders, and use of these trademarks in no way indicates any relationship between Cofense and the holders of the trademarks.