Detection: Executable File Written in Administrative SMB Share

Description

The following analytic identifies executable files (.exe or .dll) being written to Windows administrative SMB shares (Admin$, IPC$, C$). This represents suspicious behavior as its commonly used by tools like PsExec/PaExec and others to stage service binaries before creating and starting a Windows service on remote endpoints. Red Teams and adversaries alike may abuse administrative shares for lateral movement and remote code execution. The Trickbot malware family also implements this behavior to try to infect other machines in the infected network.

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Implementation

To successfully implement this search, you need to be ingesting Windows Security Event Logs with 5145 EventCode enabled. The Windows TA is also required. Also enable the object Audit access success/failure in your group policy.

Known False Positives

System Administrators may use looks like PsExec for troubleshooting or administrations tasks. However, this will typically come only from certain users and certain systems that can be added to an allow list.

Associated Analytic Story

• Active Directory Lateral Movement

• Prestige Ransomware

• Graceful Wipe Out Attack

• Industroyer2

• IcedID

• Data Destruction

• Hermetic Wiper

• Trickbot

Risk Based Analytics (RBA)

References

• https://attack.mitre.org/techniques/T1021/002/

• https://www.rapid7.com/blog/post/2013/03/09/psexec-demystified/

• https://labs.vipre.com/trickbot-and-its-modules/

• https://whitehat.eu/incident-response-case-study-featuring-ryuk-and-trickbot-part-2/

• https://thedfirreport.com/2023/05/22/icedid-macro-ends-in-nokoyawa-ransomware/

Version: 1