Match Winsock 2 API library declaration

Hunt Hypothesis

Adversaries may use Winsock 2 API declarations to establish covert network communication channels, which can be a sign of malicious network activity. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify potential command and control infrastructure or data exfiltration attempts.

YARA Rule

rule Str_Win32_Winsock2_Library
{
    meta:
        author = "@adricnet"
        description = "Match Winsock 2 API library declaration"
        method = "String match"
        reference = "https://github.com/dfirnotes/rules"

    strings:
        $ws2_lib = "Ws2_32.dll" nocase
        $wsock2_lib = "WSock32.dll" nocase

    condition:
        (any of ($ws2_lib, $wsock2_lib))
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 2 string patterns in its detection logic.

References

• https://github.com/dfirnotes/rules
• Source Rule

False Positive Guidance

• Scenario: A system administrator is using PowerShell to script network configuration changes that include Winsock 2 API calls.
  Filter/Exclusion: Exclude processes initiated by powershell.exe with a command line containing netsh or Set-NetAdapter.

• Scenario: A scheduled task runs a legitimate network diagnostic tool like Wireshark or tcpdump (on Linux) that uses Winsock 2 APIs for packet capture.
  Filter/Exclusion: Exclude processes associated with scheduled tasks that have a known benign command line or are running under a trusted user account.

• Scenario: A Windows Update or Group Policy client service is using Winsock 2 APIs to communicate with Microsoft servers during policy synchronization.
  Filter/Exclusion: Exclude processes with the image name svchost.exe or wuauclt.exe that are associated with Windows Update services.

• Scenario: A remote desktop session or Terminal Services client is establishing a network connection using Winsock 2 APIs for RDP communication.
  Filter/Exclusion: Exclude processes with the image name mstsc.exe or tsclient.exe that are part of a legitimate remote access session.

• Scenario: A network monitoring tool like Microsoft Network Monitor or SolarWinds Network Performance Monitor is using Winsock 2 APIs to capture and analyze network traffic.
  Filter/Exclusion: Exclude processes with known monitoring tool names such as nmm.exe or SolarWinds.exe that are running under a monitored system.