Detection of Windows Private Key Discovery Activity

Adversaries often perform discovery operations to locate sensitive files stored on an endpoint after initial access. This behavior frequently involves searching for various private key file formats, such as .key, .pfx, .pem, and .gpg, which can be leveraged to compromise encrypted communications, gain unauthorized access to remote services, or escalate privileges. Post-exploitation tools like WinPEAS automate this process, scanning directories for certificates and configuration files that contain sensitive credentials. Defenders can monitor for these activities by focusing on the execution of legitimate Windows binaries like cmd.exe, powershell.exe, and findstr.exe when they are invoked with command-line arguments containing specific file extension patterns indicative of private key material. This activity is a critical indicator of post-exploitation reconnaissance and warrants immediate investigation to prevent lateral movement or further environment compromise.

Attack Chain

1. Attacker gains initial access to a Windows endpoint.
2. Attacker deploys a post-exploitation tool or uses native binaries (cmd.exe, powershell.exe).
3. Attacker executes discovery commands targeting the local filesystem to find key-related files.
4. Binary (e.g., findstr.exe or powershell.exe) performs recursive directory searches for specific extensions (e.g., .pem, .pfx, .key).
5. Attacker captures the output of these discovery commands to identify the location of insecurely stored keys.
6. Attacker reads or exfiltrates the identified private keys.
7. Attacker uses stolen credentials to maintain persistence, escalate privileges, or move laterally within the network.

Impact

The discovery of private keys can lead to significant security breaches, including unauthorized access to authenticated services, decryption of sensitive traffic, and persistent unauthorized access to the environment. This activity is frequently observed in campaigns involving ransomware (e.g., Prestige Ransomware) and general-purpose post-exploitation frameworks where attackers seek to maximize the value of compromised hosts.

Recommendation

1. Deploy the provided Sigma rule to detect suspicious command-line patterns associated with key discovery.
2. Enable Sysmon Event ID 1 or Windows Security Event ID 4688 to capture comprehensive process creation telemetry, including the full command line.
3. Map process logs to the CIM Endpoint data model to ensure consistency across security analytics and dashboards.
4. Investigate any findings from the detection rule by inspecting the command-line arguments to determine the intent of the execution.