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Recommendations from our Threat Response Unit (TRU) Team:
Indicators of Compromise
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In TRU Positives, eSentire’s Threat Response Unit (TRU) provides a summary of a recent threat investigation. We outline how we responded to the confirmed threat and what recommendations we have going forward.
Here’s the latest from our TRU Team…
What did we find?
In early September 2023, we received notifications of a phishing campaign targeting the finance industry, with approximately 300 users affected.
The phishing email contained an HTML file. When this file is opened, it communicates with the attacker’s server, which then prompts the user to input their credentials into a fake Microsoft login page.
Depending on the user’s location, the attacker’s server will either display a fake loading page or a deceptive “404 Not Found” error page.
Figure 1: Fake Microsoft login page
The entered credentials would be posted to an attacker’s C2 server (in our sample, it’s h40pbqrb5ra.lopapscop[.]ws).
Looking at the source code of the HTML file, we noticed that the script is using the CryptoJS library to decrypt the encrypted data using the AES algorithm in CBC mode with PKCS#7 padding, as shown below, where the value “WPfkidgH” would contain the hardcoded email address.
Figure 2: Obfuscated code
Upon decrypting the code, we see that most of the content is in a hexadecimal format.
Further decoding, we can see the series of strings under the variable var _0xe53b. We can map the strings to specific variables within the deobfuscated code, and we will get a clear understanding of the code’s functionality, as shown below.
Figure 3: Snippet of the deobfuscated and mapped strings
Looking at the code, we can see that it implements various anti-analysis / evasion techniques, such as:
Keyboard shortcuts blocking: The code sets up keyboard shortcuts like Ctrl+U, Meta+Alt+U, Ctrl+Shift+I, Ctrl+Shift+J, and Ctrl+Shift+C to do nothing, essentially trying to disable the usual ways to open browser developer tools or view page source.
Context Menu Blocking: The right-click context menu is disabled, making it not possible to inspect elements via right-clicking.
Triggering the "Hmmm .." alert under certain conditions:
Accessing the message property of the error object, which is achieved by using Object.defineProperties function that modifies properties of the error object to show the "Hmmm .." alert when its message property is accessed.
Calling the “toString” method of the error object – if an error's stack includes the string "toString@", the "Hmmm .." alert will be displayed. So, if someone tries to inspect the error object in the developer console or if certain operations within the developer tools attempt to convert the error object to a string, the alert is displayed. That likely explains why the pop-up message is displayed when the Developer Tool is opened in the browser.
Randomized URLs – URLs are generated using random strings, which can make static analysis harder. The randomly generated strings are prepended to “lopapscop[.]ws/obufsssssssscaaatoion" or “jdjdmxnx[.]online/obufsssssssscaaatoion”
Displaying the loading screen or “404 Not Found” error.
For “Displaying the loading screen or “404 Not Found” error anti-analysis / evasion technique, the code gathers the data of the machine via the API request to https://pro.ip-api[.]com/json/?key=pD3jjrEbn4o2CQ1
and then sends the data in a JSON format to the server (for example, enwpcfr7me.lopapscop[.]ws/obufsssssssscaaatoion/ or .wtis4sz9mjF/jdjdmxnx[.]online/obufsssssssscaaatoion/) as shown in Figure 4.
Figure 4: Data being sent to the server
The ‘NAMEOFTHEGUY’ (Figure 4) contains likely the threat actor’s handle for the phishing campaign, in our case it’s “Waaaa.004.aavy”.
Upon the returned data from POST request, the function checks a returned property named "Allow_Online" that is received from the server. Based on its value, it takes different actions:
If the URL (_0x9ce1x1a) starts with "http://" or "https://" and if Allow_Online is "Yes" – it hides the "loadingScreen".
If Allow_Online is "No" – it doesn't do anything in this scenario.
If the current URL (_0x9ce1x1a) does NOT start with "http://" or "https://" and if Allow_Online is "No" then it hides the "loadingScreen".
If Allow_Online is "Both" regardless of the URL, it hides the "loadingScreen".
If Allow_Online is "404 Not Found" – it hides the "loadingScreen" and displays a "404 Not Found" message.
Additionally, if the current location's hostname is "localhost" or "127.0.0.1", a message "Don't run me here!" is logged to the console.
Figure 5: Image of the "loadingScreen"
Upon further investigation of the domains, we discovered more than a thousand associated phishing pages on URLScan.
Figure 6: Related phishing landing pages
What did we do?
We investigated the incident and confirmed the activity is malicious.
Our team of 24/7 Cyber SOC Analysts recommended that the client reset their credentials and block the malicious domains.
What can you learn from this TRU positive?
Various anti-analysis / evasion techniques are implemented within the phishing landing page, including various attempts to prevent or deter developers from using browser developer tools and inspecting the code.
This includes blocking key combinations commonly associated with such tools and displaying misleading messages if specific conditions are met.
Variable names and functions are encrypted and obfuscated, making it harder to quickly understand the purpose and behavior of the code.
Recommendations from our Threat Response Unit (TRU) Team:
The eSentire Threat Response Unit (TRU) is an industry-leading threat research team committed to helping your organization become more resilient. TRU is an elite team of threat hunters and researchers that supports our 24/7 Security Operations Centers (SOCs), builds threat detection models across the eSentire XDR Cloud Platform, and works as an extension of your security team to continuously improve our Managed Detection and Response service. By providing complete visibility across your attack surface and performing global threat sweeps and proactive hypothesis-driven threat hunts augmented by original threat research, we are laser-focused on defending your organization against known and unknown threats.
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