T1021.002_smbwindows-admin-shares

T1021.002 SMB/Windows Admin Shares

Sub-technique of: T1021

High-Level Description

Adversaries may use Valid Accounts to interact with a remote network share using Server Message Block (SMB). The adversary may then perform actions as the logged-on user.

SMB is a file, printer, and serial port sharing protocol for Windows machines on the same network or domain. Adversaries may use SMB to interact with file shares, allowing them to move laterally throughout a network. Linux and macOS implementations of SMB typically use Samba.

Windows systems have hidden network shares that are accessible only to administrators and provide the ability for remote file copy and other administrative functions. Example network shares include C$, ADMIN$, and IPC$. Adversaries may use this technique in conjunction with administrator-level Valid Accounts to remotely access a networked system over SMB, to interact with systems using remote procedure calls (RPCs), transfer files, and run transferred binaries through remote Execution. Example execution techniques that rely on authenticated sessions over SMB/RPC are Scheduled Task/Job, Service Execution, and Windows Management Instrumentation. Adversaries can also use NTLM hashes to access administrator shares on systems with Pass the Hash and certain configuration and patch levels.

Kill Chain Phase

• Lateral Movement (TA0008)

Platforms: Windows

What to Check

• Identify if SMB/Windows Admin Shares technique is applicable to target environment
• Check Windows systems for indicators of SMB/Windows Admin Shares
• Verify mitigations are bypassed or absent (4 known mitigations)
• Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: Map admin share

Connecting To Remote Shares

Supported Platforms: windows

cmd.exe /c "net use \\#{computer_name}\#{share_name} #{password} /u:#{user_name}"

Atomic Test 2: Map Admin Share PowerShell

Map Admin share utilizing PowerShell

Supported Platforms: windows

New-PSDrive -name #{map_name} -psprovider filesystem -root \\#{computer_name}\#{share_name}

Atomic Test 3: Copy and Execute File with PsExec

Copies a file to a remote host and executes it using PsExec. Requires the download of PsExec from https://docs.microsoft.com/en-us/sysinternals/downloads/psexec.

Supported Platforms: windows Elevation Required: Yes

"#{psexec_exe}" #{remote_host} -accepteula -c #{command_path}

Dependencies:

• PsExec tool from Sysinternals must exist on disk at specified location (#{psexec_exe})

Atomic Test 4: Execute command writing output to local Admin Share

Executes a command, writing the output to a local Admin Share. This technique is used by post-exploitation frameworks.

Supported Platforms: windows Elevation Required: Yes

cmd.exe /Q /c #{command_to_execute} 1> \\127.0.0.1\ADMIN$\#{output_file} 2>&1

Manual Testing

If Atomic Red Team tests are not applicable, manually verify the technique by:

1. Identify Attack Surface: Determine if the target environment is susceptible to SMB/Windows Admin Shares by examining the target platforms (Windows).

2. Assess Existing Defenses: Review whether mitigations for T1021.002 are in place. If defenses are absent or misconfigured, this technique may be exploitable.

3. Execute Test: Use tools and methods described in the MITRE ATT&CK page and external references below.

Remediation Guide

M1026 Privileged Account Management

Deny remote use of local admin credentials to log into systems. Do not allow domain user accounts to be in the local Administrators group multiple systems.

M1035 Limit Access to Resource Over Network

Consider disabling Windows administrative shares.

M1037 Filter Network Traffic

Consider using the host firewall to restrict file sharing communications such as SMB.

M1027 Password Policies

Do not reuse local administrator account passwords across systems. Ensure password complexity and uniqueness such that the passwords cannot be cracked or guessed.

Detection

Multi-Event Detection for SMB Admin Share Lateral Movement

Risk Assessment

CWE Categories

References

• Medium Detecting WMI Persistence
• TechNet RPC
• Microsoft Admin Shares
• Windows Event Forwarding Payne
• Lateral Movement Payne
• Wikipedia Server Message Block
• Atomic Red Team - T1021.002
• MITRE ATT&CK - T1021.002