Detect SMB/Windows Admin Shares in Microsoft Sentinel
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$) accessible only to administrators. Adversaries abuse these shares to copy tools, execute payloads, and move laterally throughout a network. Major ransomware families (Conti, Ryuk, NotPetya, Emotet, Royal, RansomHub) and APT groups (APT41, Sandworm, Wizard Spider, Chimera) have all leveraged SMB admin shares for lateral movement. Common execution methods paired with SMB include PsExec, scheduled tasks, service creation, and WMI.
MITRE ATT&CK
- Tactic
- Lateral Movement
- Technique
- T1021 Remote Services
- Sub-technique
- T1021.002 SMB/Windows Admin Shares
- Canonical reference
- https://attack.mitre.org/techniques/T1021/002/
KQL Detection Query
// Detect suspicious SMB admin share access and lateral tool transfer
DeviceNetworkEvents
| where Timestamp > ago(24h)
| where RemotePort == 445
| where ActionType in ("ConnectionSuccess", "ConnectionFound")
// Exclude known legitimate management traffic
| where not (InitiatingProcessFileName in~ ("svchost.exe", "System") and RemotePort == 445)
| extend IsAdminShare = InitiatingProcessCommandLine has_any ("ADMIN$", "C$", "IPC$", "\\\\")
| project Timestamp, DeviceName, InitiatingProcessFileName, InitiatingProcessCommandLine,
RemoteIP, RemotePort, RemoteUrl, ActionType
| union (
// Detect PsExec-style service creation over SMB
DeviceProcessEvents
| where Timestamp > ago(24h)
| where FileName in~ ("psexec.exe", "psexec64.exe", "paexec.exe", "remcom.exe")
| extend Source = "PsExec"
| project Timestamp, DeviceName, InitiatingProcessFileName, ProcessCommandLine,
AccountName, Source
)
| union (
// Detect net use commands establishing share connections
DeviceProcessEvents
| where Timestamp > ago(24h)
| where FileName =~ "net.exe" or FileName =~ "net1.exe"
| where ProcessCommandLine has "use" and ProcessCommandLine has_any ("ADMIN$", "C$", "IPC$", "\\\\")
| project Timestamp, DeviceName, InitiatingProcessFileName, ProcessCommandLine, AccountName
)
| sort by Timestamp descDetects SMB-based lateral movement via three patterns: outbound connections to port 445 from non-system processes, execution of PsExec/PaExec tools used to run commands on remote systems via ADMIN$, and 'net use' commands mapping administrative shares (C$, ADMIN$, IPC$). Uses DeviceNetworkEvents and DeviceProcessEvents from Microsoft Defender for Endpoint.
Data Sources
Required Tables
False Positives & Tuning
- SCCM/Intune agents distributing software packages via ADMIN$ shares to managed endpoints
- Backup agents (Veeam, NetBackup, Commvault) accessing C$ for backup operations
- IT administrators manually copying files to ADMIN$ for troubleshooting or patching
- Legitimate PsExec use by sysadmins for remote command execution on managed hosts
- Windows file sharing between workstations in peer-to-peer environments or home networks
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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