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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…
The first stage PowerShell script is responsible for executing an XOR-Encrypted C# source file that is decompiled to install the ChromeLoader extension from registry (Figures 3 and 4).
The decryption routine base64 decodes then takes the first 5 bytes from the XOR-encrypted registry value. These bytes are used as a key to XOR a string (in this case “Get-ItemPropertyValue”) which is base64 encoded. The resulting 28-character key is then used to decrypt the C# source file (minus the first 5 bytes) and the code is executed. The PowerShell script also contains redundancy to retrieve code from the C2 (hxxps://evelopedsev[.]autos in this case) and write it to the registry should it be missing or removed.
Examining the cleartext C# source file shows how the Chrome extension is loaded via PowerShell. The code contains a JSON list object which is base64 encoded and XOR-encrypted using similar logic to the function above. In this case, the first 5 bytes of the encrypted JSON object are used as a key. The resulting list items (Figure 5) are then passed as arguments to the Start-Process cmdlet.
PowerShell will attempt to start Chrome from various paths using the “load-extension” argument to load the “chrome_data” extension (Figure 6). It also contains logic to replace this name with others in the list below.
The extension files (Figure 7) are stored in C:\Users\user\AppData\Local\chrome_data (or another name from the list above). The code contains logic to retrieve a new copy of the extension in from asanttackl[.]autos if removed.
The ChromeLoader extension contains high privileges, such as reading browsing history, managing apps/extensions, page content manipulation, etc. (Figure 8). These privileges are core to its functionality, mainly serving ads and capturing browser history/search terms (Figure 9). It also attempts to block the user from editing Chrome extensions to hinder removal.
eSentire’s Threat Response Unit (TRU) is a world-class team of threat researchers who develop new detections enriched by original threat intelligence and leverage new machine learning models that correlate multi-signal data and automate rapid response to advanced threats.
If you are not currently engaged with an MDR provider, eSentire MDR can help you reclaim the advantage and put your business ahead of disruption.
Learn what it means to have an elite team of Threat Hunters and Researchers that works for you. Connect with an eSentire Security Specialist.
|10CE7795E0D7D0AACB487A3C67A2F59F||ChromeLoader Stage 1 PowerShell|
|EA0FCD070E59389EEA6C280B5B582A18||ChromeLoader XOR-encrypted C# Source File|
|5DEFEA9D05D5A2EBB03FBEAC464A948A||ChromeLoader C# Source File|
|evelopedsev[.]autos||C2 Domain (Stage 1 PowerShell)|
|asanttackl[.]autos||C2 Domain (C# Source File)|
|usesianeduke[.]xyz||C2 Domain (Browser Extension)|
Our industry-renowned Threat Response Unit (TRU) is an elite team of threat hunters and researchers, that supports our 24/7 Security Operations Centers (SOCs), builds detection models across our Atlas XDR Cloud Platform, and works as an extension of your security team to continuously improve our Managed Detection and Response service. TRU has been recognized for its threat hunting, original research and content development capabilities. TRU is strategically organized into cross-functional groups to protect you against advanced and emerging threats, allowing your organization to gain leading threat intelligence and incredible cybersecurity acumen.