New Project CAV3RN module abuses Outlook calendar events for C2 and DNS AAAA records for configuration recovery
July 21, 2026 · Kaspersky (Securelist) · Severity: MEDIUM
In June 2026, Kaspersky researchers identified a new module within the Project CAV3RN framework, a sophisticated cyberespionage tool targeting Israeli entities. This module, designed to replace the previous HTTP/WebSocket communication component, leverages Microsoft Outlook calendar events accessed via Microsoft Graph for command-and-control (C2) operations. If authentication or tenant validation fails, the module retrieves connection settings through DNS AAAA records. This shift highlights the attackers' evolving tactics to maintain stealth and resilience. The module, named AzureCommunication.dll, is compiled using .NET Native AOT, making it harder to analyze by removing metadata and intermediate language typically present in .NET assemblies. It operates within a controller-based architecture, where the controller (uxtheme.dll) manages tasks and dispatches commands to plugins. The module’s functionality is exposed through a single export, QueryInterface, which processes commands and results using a specific input format. It maintains compatibility with the previous controller while obtaining its configuration from Microsoft Graph. The DLL contains a default configuration, including Microsoft Entra tenant ID, application credentials, and cryptographic keys, which it writes to a file named logAzure.txt if not already present. This innovative use of Outlook calendar events for C2 communication underscores the attackers' creativity in exploiting legitimate services to evade detection. The targeting of Israeli organizations and the framework's modular nature suggest a focus on persistent, adaptable espionage campaigns. This development is significant as it demonstrates the increasing sophistication of cyberespionage tools and the potential for abuse of widely used platforms like Microsoft 365.
Introduction
In June 2026, as part of our Kaspersky Threat Intelligence Reporting service, we published extensive research on Project CAV3RN, a sophisticated modular framework used for cyberespionage activity against targets in Israel. We have been tracking this cluster since December 2025, and in late April 2026, we observed a major architectural shift: the developers moved from a three-component framework consisting of a downloader, executor, and uploader to a controller-based architecture with a dedicated WebSocket-enabled C2 communication component and a more extensible plugin system designed to support modular post-exploitation capabilities.
Subsequently, Check Point Research publicly reported on the same controller-based architecture in July 2026. However, neither our previous research nor the subsequent public reporting covered the latest communication component analyzed in this report.
Following our June 2026 publication, we identified a .NET Native AOT communication module that is apparently designed to replace the previous HTTP/WebSocket component. It exchanges commands and results through Outlook calendar events accessed via Microsoft Graph. If Microsoft Graph authentication or tenant validation fails, the module attempts to retrieve replacement connection settings through DNS AAAA responses.
Module network communication architecture
During the preparation of this report, additional public research covering this communication component became available. The research presented in our article is based on our independent analysis and includes several additional implementation details that complement the existing public reporting.
Technical details
The previously reported controller-based CAV3RN architecture separates C2 communication from command execution. The controller, uxtheme.dll, generates and maintains the seven-character Agent ID, manages the polling loop, processes built-in commands, and dispatches other tasks or commands to separate plugins. The previously used communication component, n-HTCommp.dll, retrieved commands and transmitted execution results over HTTP/WebSocket.
Project CAV3RN architecture (April 2026)
The module performs the same communication role but uses Outlook calendar events accessed through Microsoft Graph. Similarly to the previous version, its get and send interface and use of the same controller-generated Agent ID suggest that it was designed to replace the previous communication component. However, because the corresponding updated controller was not recovered, this replacement role is assessed rather than directly observed.
C2 communication module
The communication module, AzureCommunication.dll, is a DLL compiled with .NET Native AOT, consistent with several other components of the Project CAV3RN framework that are publicly documented. Such a compilation method turns the managed application into native machine code and removes most of the metadata and intermediate language that normally make .NET assemblies straightforward to analyze.
The module exposes its functionality through a single export named QueryInterface. We expect an updated controller to load the DLL, resolve this export, and pass it a null-terminated UTF-16 string. The accepted input format closely follows the interface used by the previously documented CAV3RN controller.
get_;;_<agent-id>_,_<legacy-url> send_;;_<agent-id>_,_<legacy-url>_,_<result>
The _;;_ delimiter separates the operation from its arguments, while _,_ separates the arguments.
For get, the module only uses the first argument as the Agent ID. For send, it uses only the Agent ID and the result. In both cases, the additional legacy URL is ignored. It remains part of the interface for compatibility with the controller, even though the new module obtains its destination and credentials from its own Microsoft Graph configuration.
Outlook calendar events as a C2 channel
The DLL contains a complete default configuration, including the Microsoft Entra tenant ID, application credentials, target mailbox, DNS bootstrap host, and cryptographic keys required to establish communication.
Before processing either get or send operation, the module looks for a relative file named logAzure.txt. Because the code supplies only a filename, Windows resolves it against the current working directory of the process hosting the DLL.
If logAzure.txt exists, the module reads and deserializes it. If it is absent, the module builds the configuration from the hardcoded values and writes the complete object to disk with the following structure:
{
"TenantId": "******-****-****-****-**********", // Microsoft Entra tenant ID
"ClientId": "********-****-****-****-************", // application/client ID
"ClientSecret": "********************************************",
"UserEmail": "***@*********.co.il", // Compromised target Microsoft 365 mailbox
"Host": "cloudlanecdn[.]com", // DNS bootstrap domain
"PublicKey": "-----BEGIN RSA PUBLIC KEY-----\r\n[omitted]\r\n-----END RSA PUBLIC KEY-----", // outbound encryption public key
"PrivateKey": "-----BEGIN RSA PRIVATE KEY-----\r\n[omitted]\r\n-----END RSA PRIVATE KEY-----" // inbound decryption private key
}Using the resulting configuration, the module creates a Microsoft Graph client and validates access by requesting the tenant’s organization record through a GET request to https://graph.microsoft.com/v1.0/organizationKey Takeaways