Threat actors are increasingly exploiting Windows Remote Management (WinRM) to navigate through Active Directory (AD) environments with a level of stealth that allows them to bypass conventional detection systems. This method not only facilitates privilege escalation but also enables the deployment of malicious payloads.
WinRM, which is Microsoft’s implementation of the WS-Management protocol, serves as a fundamental component of Windows systems. It empowers administrators to execute remote commands, manage configurations, and run PowerShell scripts across the network. By default, WinRM operates on HTTP port 5985 and HTTPS port 5986, permitting authenticated users to initiate sessions and perform management tasks remotely.
While designed for legitimate remote administration, the widespread use of WinRM, coupled with its integration with PowerShell, makes it an attractive target for attackers aiming to gain lateral movement capabilities. Once valid credentials are compromised—often through phishing, credential dumping, or brute-force attacks—attackers can leverage WinRM to execute arbitrary commands or scripts on other systems within the AD domain.
Attack Chain of a WinRM-Based Attack
The attack chain typically unfolds in several stages:
- Initial Access: The attacker secures a foothold on a single endpoint, often masquerading as a standard domain user.
- Reconnaissance: Utilizing WinRM-enabled PowerShell commands such as Invoke-Command and Enter-PSSession, the attacker scans for accessible systems by probing for open ports 5985 and 5986.
With valid credentials in hand, the attacker can authenticate to remote systems, initiating new PowerShell sessions. Each session operates under the wsmprovhost.exe process within the user’s context, allowing it to blend seamlessly into routine administrative activities.
Payload Deployment: Attackers then deploy malicious payloads using sophisticated techniques like PowerShell cradles or reflective .NET module loaders. These methods effectively obfuscate the payload, circumventing the Antimalware Scan Interface (AMSI) and disabling event logging to evade detection.
Persistence and Lateral Movement: By repeating this process, attackers can traverse the network laterally, escalating their privileges and targeting high-value assets, including domain controllers. They often generate an obfuscated PowerShell script (the “cradle”) that downloads and executes additional payloads directly in memory, significantly reducing forensic traces.
In the reflective .NET module loader method, attackers pass a compiled .NET assembly as an argument to a seemingly benign PowerShell script, which then loads and executes the module reflectively. This technique camouflages malicious code within legitimate administrative scripts, complicating detection efforts.
Mitigation
Security experts caution that detecting WinRM-based lateral movement poses significant challenges, as it utilizes built-in Windows functionalities and often operates over encrypted channels. Nevertheless, defenders can monitor for anomalous usage patterns, including:
- Unexpected instances of wsmprovhost.exe processes.
- Unusual remote PowerShell activity.
- Authentication attempts originating from non-administrative accounts.
- High volumes of traffic on ports 5985 and 5986.
Organizations are encouraged to restrict access to WinRM, enforce robust credential hygiene, and implement advanced monitoring solutions capable of correlating indicators of lateral movement across their networks.
