Detect SMB/Windows Admin Shares in CrowdStrike LogScale
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$) accessible only to administrators. Adversaries abuse these shares to copy tools, execute payloads, and move laterally throughout a network. Major ransomware families (Conti, Ryuk, NotPetya, Emotet, Royal, RansomHub) and APT groups (APT41, Sandworm, Wizard Spider, Chimera) have all leveraged SMB admin shares for lateral movement. Common execution methods paired with SMB include PsExec, scheduled tasks, service creation, and WMI.
MITRE ATT&CK
- Tactic
- Lateral Movement
- Technique
- T1021 Remote Services
- Sub-technique
- T1021.002 SMB/Windows Admin Shares
- Canonical reference
- https://attack.mitre.org/techniques/T1021/002/
LogScale Detection Query
#event_simpleName in ["ProcessRollup2", "NetworkConnectIP4"]
| case {
FileName = /(?i)^(psexec64?|paexec|remcom)\.exe$/ |
alert_type := "PsExecExecution" ;
FileName = /(?i)^net1?\.exe$/ |
CommandLine = /(?i)\buse\b/ |
CommandLine = /(?i)(ADMIN\$|IPC\$|C\$)/ |
alert_type := "NetUseAdminShare" ;
#event_simpleName = "NetworkConnectIP4" |
RemotePort = "445" |
FileName != "svchost.exe" |
FileName != "System" |
alert_type := "SMB445Connection" ;
* | drop()
}
| table([@timestamp, ComputerName, UserName, FileName, CommandLine, RemoteAddressIP4, RemotePort, alert_type], limit=1000, sortby=@timestamp, order=desc)CrowdStrike Falcon LogScale (CQL) query using ProcessRollup2 (process creation telemetry) and NetworkConnectIP4 (outbound network connection) Falcon sensor events to detect three admin share abuse patterns. Case branching classifies events as PsExecExecution (psexec/paexec/remcom tool launch), NetUseAdminShare (net use commands targeting ADMIN$, C$, or IPC$), or SMB445Connection (non-system process connecting outbound to port 445). Requires Falcon Insight XDR or Falcon Endpoint Protection with full process and network telemetry enabled.
Data Sources
Required Tables
False Positives & Tuning
- CrowdStrike Falcon's own Real Time Response (RTR) capability uses SMB for file transfer operations during live response sessions; NetworkConnectIP4 events on port 445 originating from the Falcon sensor process (CSFalconService.exe) should be explicitly excluded
- PsExec is widely used by IT administrators for authorized remote management; in environments where psexec is sanctioned, enrich detections with user context and restrict alerting to non-privileged accounts or unusual source systems not in the IT asset list
- Backup and monitoring agents (SolarWinds, PRTG, Zabbix, Veeam) that poll remote hosts via SMB or use administrative shares for data collection will generate NetworkConnectIP4 events on port 445 at regular intervals; whitelist known monitoring infrastructure by source hostname or IP
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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