Detect SMB/Windows Admin Shares in Splunk
Adversaries may use Valid Accounts to interact with a remote network share using Server Message Block (SMB). Windows systems have hidden administrative shares (C$, ADMIN$, IPC$) accessible only to administrators. Adversaries abuse these shares to copy tools, execute payloads, and move laterally throughout a network. Major ransomware families (Conti, Ryuk, NotPetya, Emotet, Royal, RansomHub) and APT groups (APT41, Sandworm, Wizard Spider, Chimera) have all leveraged SMB admin shares for lateral movement. Common execution methods paired with SMB include PsExec, scheduled tasks, service creation, and WMI.
MITRE ATT&CK
- Tactic
- Lateral Movement
- Technique
- T1021 Remote Services
- Sub-technique
- T1021.002 SMB/Windows Admin Shares
- Canonical reference
- https://attack.mitre.org/techniques/T1021/002/
SPL Detection Query
index=wineventlog (sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" OR sourcetype="WinEventLog:Security")
(
(EventCode=5140 OR EventCode=5145)
| eval ShareName=coalesce('Share_Name', ObjectName)
| eval SourceIP=coalesce('Source_Address', IpAddress)
| eval AccessAccount=coalesce('Account_Name', SubjectAccountName)
| where ShareName IN ("\\\\*\\ADMIN$", "\\\\*\\C$", "\\\\*\\IPC$") OR match(ShareName, "\\\\\\\\.*\\\\(ADMIN|C|IPC)\\$")
| eval AlertType="AdminShareAccess"
| table _time, host, ShareName, SourceIP, AccessAccount, AlertType
)
OR
(
sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=1
(Image="*\\psexec.exe" OR Image="*\\psexec64.exe" OR Image="*\\paexec.exe" OR Image="*\\remcom.exe")
| eval AlertType="PsExecExecution"
| table _time, host, Image, CommandLine, User, AlertType
)
OR
(
sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=1
(Image="*\\net.exe" OR Image="*\\net1.exe")
CommandLine="*use*"
(CommandLine="*ADMIN$*" OR CommandLine="*C$*" OR CommandLine="*IPC$*")
| eval AlertType="NetUseAdminShare"
| table _time, host, Image, CommandLine, User, AlertType
)
| sort - _timeDetects SMB admin share lateral movement using three log sources: Security Event 5140/5145 (share access to ADMIN$, C$, IPC$), Sysmon Event 1 for PsExec/PaExec process creation, and Sysmon Event 1 for net use commands targeting admin shares. Combines Windows Security log share audit events with Sysmon process telemetry.
Data Sources
Required Sourcetypes
False Positives & Tuning
- SCCM/Intune agents distributing software packages via ADMIN$ shares
- Backup agents accessing C$ for backup operations
- IT administrators manually copying files to ADMIN$ for patching
- Legitimate PsExec use by sysadmins for remote command execution
- Windows file sharing between workstations
Other platforms for T1021.002
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Map Admin Share with Net Use
Expected signal: Sysmon Event ID 1: net.exe with CommandLine containing 'use' and 'C$'. Sysmon Event ID 3: Network Connection to 127.0.0.1:445. Security Event ID 4624 (LogonType=3, NTLM or Kerberos) on the target. Security Event ID 5140 (share accessed: \\*\C$).
- Test 2Copy File to ADMIN$ Share
Expected signal: Sysmon Event ID 3: Network Connection to 127.0.0.1:445 from cmd.exe. Security Event ID 5145: Detailed network share file access for \\*\ADMIN$\calc_test.exe. Sysmon Event ID 11: File created at C:\Windows\calc_test.exe on the target.
- Test 3PsExec Remote Command Execution via ADMIN$
Expected signal: Sysmon Event ID 1: psexec.exe process creation. Sysmon Event ID 11: PSEXESVC.exe file created in C:\Windows\. Security Event ID 7045: New service 'PSEXESVC' installed. Security Event ID 4624 (LogonType=3) on the target. Security Event ID 5140 (\\*\ADMIN$ accessed).
- Test 4Enumerate Admin Shares with Net View
Expected signal: Sysmon Event ID 1: net.exe with CommandLine 'view \\127.0.0.1 /all'. Sysmon Event ID 3: Network Connection to 127.0.0.1:445. Security Event ID 5140 (IPC$ share access for enumeration).
References (8)
- https://attack.mitre.org/techniques/T1021/002/
- https://docs.microsoft.com/en-us/windows-server/storage/file-server/troubleshoot/detect-enable-and-disable-smbv1-v2-v3
- https://learn.microsoft.com/en-us/sysinternals/downloads/psexec
- https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-5140
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1021.002/T1021.002.md
- https://docs.microsoft.com/en-us/archive/blogs/jepayne/tracking-lateral-movement-part-one-special-groups-and-specific-service-accounts
- https://www.cybereason.com/blog/research/cybereason-vs-conti-ransomware
- https://medium.com/threatpunter/detecting-removing-wmi-persistence-60ccbb7dff96
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