The Emotet malware is a very destructive banking Trojan that was first identified in 2014. Over the years it has evolved with new capabilities and functionalities, prompting cybersecurity agencies like the Australian Cyber Security Centre and US-CERT to issue advisories. Emotet malware generally spreads via malicious documents that drop a modular Trojan bot, which is used to download and install additional remote access tools. We wrote a blog post in January 2019 about how the malware had changed tactics, leading to a spike in the number of Emotet malware attacks. In the last week, we have observed a spike in the number of Emotet malware transactions across our customer base. US-CERT has also issued a fresh advisory regarding the recent spate of attacks.
Our research has discovered that the Emotet malware is still very active and continues to be one of the most destructive malware attacks. The malware has evolved through the years, and the actors behind Emotet have used the infected endpoints to build out a formidable botnet that is used to distribute multiple malware families such as Trickbot and Dridex, as well as ransomware such as Ryuk.
After taking a break through the holiday season in 2019, Emotet malware attacks have restarted in 2020, this time targeting the financial services industry. Similar to previous versions, the Emotet malware is only just the initial attack vector used to launch the attack. The attack is initiated with a malicious Microsoft Word document that is designed to be downloaded and opened by the user. Once opened, the malicious macro executes and contact is made with the command-and-control server to initiate the next stage of the attack.
Menlo Security Research analyzed the topics listed below to gain a better understanding of this most recent Emotet malware attack. Data for this analysis was obtained from the Menlo Security Cloud Platform, which supports millions of users across all industries, including financial services, educational institutions, and the military. In addition to analyzing the Emotet document macro and loader, the analysis breaks down the following for this most recent Emotet malware attack spike and shows the distribution of the industries affected.
- Emotet Kill Chain
- Industries targeted
- Distribution of Emotet hosting domains
- Emotet controller IP distribution
Recent news shows that Emotet infections have crippled daily operations in a number of organizations. Emotet usually propagates in bursts, through delivery of malicious documents via mass compromised websites. Each infected host is then used to build out a botnet. The Menlo Security Research team noticed a spike in Emotet malware activity in January 2020. This spike was detected through our cloud isolation platform, which renders email attachments and websites visited from emailed links remotely, eliminating the possibility that malicious documents would reach an end user’s computer.
The spike in activity occurred during January 14–22, affecting customers using our isolation service in the United States, Europe, and Asia. The following chart shows a spike in the number of Emotet document requests from January 14–22, 2020.
The chart above shows a Spike in Emotet Malware Detected
The Emotet Kill Chain
Like other Emotet malware versions, this recent attack also used malicious macros in a Microsoft Word document. The emails were crafted to appear as legitimate banking or financial transactions. Some examples of the subject lines used in this most recent campaign are given below.
The January 2020 campaign appeared to follow the kill chain similar to the attacks observed in late 2019. The initial attack is used only to gain a foothold in the network and establish contact with the command-and-control server. Once in place, additional malware is downloaded and the malware attempts to spread to other computers on the same network.
Emotet Malware Kill Chain
From the above flow, we can divide the Emotet kill chain as follows:
- Hosting of malicious documents via compromised websites.
- Every malicious document has an embedded macro with a list of stage one URLs to try (usually three or four in the list, depending on the sample).
- The Emotet loader establishes a command-and-control channel by selecting a server IP from a list of built-in C2 IP addresses.
Distribution and Infrastructure
Our data shows that the January 2020 campaign targeted financial services companies primarily in the United States. The following charts show the industry/vertical distribution and regions where these requests came from. Other industries and geographies were included in the attack, though to a far lesser degree.
One of the techniques that Emotet malware uses is to distribute itself through other compromised legitimate websites, essentially creating new zero-day attacks. This makes the malware particularly difficult to protect against since the source of the malware is constantly changing. The following chart categorizes the distribution of the initial delivery URLs that served the malicious documents. The data shows very clearly why Emotet malware continues to evade security defenses and wreak havoc: 76 percent of the URLs used to distribute Emotet malware are actually categorized as safe by the leading threat intelligence databases. Some of the compromised websites were from academic institutions. This means that security products would not block or prohibit users from accessing and downloading content from these sites. Fortunately, Menlo Security customers were fully protected, because these malicious sites would have been viewed in isolation—completely protecting the end user.
Malicious Document Macro
Once the embedded macro inside the document is enabled, it spawns PowerShell to try a list of URLs to fetch the initial Emotet loader. Some observations of the macro behavior:
- The macro constructs the PowerShell command by decoding data from a user form.
- The PowerShell code is stored as a “Tag” property of a frame in the user form, and this frame is used to mask the other elements in the user form.
- The PowerShell code that finally gets executed is Base64 encoded, which tries to download the Emotet loader by trying a list of URLs.
- Uses Net.WebClient.DownloadFile to download the URL and [Diagnostics.Process]::Start to start the process if the download was successful.
Current Emotet Loader and Controller Infrastructure
Further analysis shows that the January 2020 Emotet malware was a far-reaching campaign that was executed through multiple networks. A concentration of IP addresses occurred in certain countries with global financial centers.
The final Emotet bot that gets dropped is usually a modular Trojan that establishes a command-and-control channel by choosing an IP from a list of IP addresses in its config file. The Emotet loader is very well researched and documented, so we will not get into the inner workings of this bot here. Some of the variations we observed:
- We noticed that the initial dropper copies itself to “SysWOW64” and is invoked with a parameter that looks like a random number (--94737736).
- Other characteristics exhibited were typical of a standard Emotet loader:
- Extract system information, enumerate running processes (CreateToolhelp32Snapshot), bundle it using protobuf, and encrypt using an AES key (which is secured with an embedded RSA public key).
- The encrypted POST request to the C2 IP seems to use a randomly generated string param that is form-urlencoded, which seems to be a slight change from previous payload URL patterns.
- In some of the controller IPs, we observed HTTP traffic being sent over port 443.
- A sample encrypted C2 payload is shown below:
The Emotet malware has built a formidable infrastructure over time and can be destructive to an organization if not mitigated in a timely manner. Its techniques of leveraging multistage attacks and distributing malicious code through legitimate websites make the Emotet malware particularly hard to prevent with traditional security products that rely on signatures or threat intelligence.
To protect against Emotet malware attacks, enterprises should:
- Be wary of macro-enabled, untrusted Office documents.
- Vet PowerShell execution policies for Windows users in an organization.
For threat response teams: Keep a close watch on the techniques used by the Emotet actors; https://attack.mitre.org/software/S0367/ has a specific ATT&CK framework page for Emotet.
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