Splunk Security
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This detection identifies changes to the VIB (vSphere Installation Bundle) acceptance level on an ESXi host. Modifying the acceptance level, such as setting it to CommunitySupported, lowers the system's integrity enforcement and may allow the installation of unsigned or unverified software. This action can be an indicator of an adversary attempting to install malicious VIBs for persistence or other malicious activities.
This detection identifies the execution of the Windows Remote Desktop Client (mstsc.exe) with the "/v" and /admin command-line arguments. The "/v" flag specifies the remote host to connect to, while the /admin flag initiates a connection to the target system’s console session, often used for administrative purposes. This combination may indicate that a user or attacker is performing privileged remote access, potentially to manage a system without disrupting existing user sessions. While such usage may be legitimate for IT administrators, it is less common in typical user behavior. Threat actors may abuse this capability during lateral movement to maintain stealthy access to high-value systems. Monitoring for this pattern can help detect interactive hands-on-keyboard activity, privilege abuse, or attempts to access critical infrastructure without leaving typical login traces associated with non-admin RDP sessions.
This detection identifies when the ESXi firewall is disabled or set to permissive mode, which can expose the host to unauthorized access and network-based attacks. Such changes are often a precursor to lateral movement, data exfiltration, or the installation of malicious software by a threat actor.
The analytic detects successful Remote Desktop Protocol (RDP) login sessions, identified by Windows Security Event ID 4624 with Logon Type 10. This indicates a user has successfully authenticated and established an interactive RDP session, which is a critical indicator of remote access to a Windows system. Correlating this with Event ID 1149 (RDP authentication success) helps differentiate between credential acceptance and actual session establishment.
The following analytic identifies child processes spawned by vmtoolsd.exe, the VMWare Tools service in Windows, which typically runs with SYSTEM privileges. This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process and parent process relationships. Monitoring this activity is crucial as it can indicate exploitation attempts, such as CVE-2023-20867. If confirmed malicious, attackers could gain SYSTEM-level access, allowing them to execute arbitrary code, escalate privileges, and potentially compromise the entire system.
This detection identifies the use of ESXCLI commands to discover virtual machines on an ESXi host. While used by administrators, this activity may also indicate adversary reconnaissance aimed at identifying high value targets, mapping the virtual environment, or preparing for data theft or destructive operations.
This analytic monitors Windows RDP client connection sequence events (EventCode 1024) from the Microsoft-Windows-TerminalServices-RDPClient/Operational log. These events track when RDP ClientActiveX initiates connection attempts to remote servers. The connection sequence is a critical phase of RDP where the client and server exchange settings and establish common parameters for the session. Monitoring these events can help identify unusual RDP connection patterns, potential lateral movement attempts, unauthorized remote access activity, and RDP connection chains that may indicate compromised systems.
This detection identifies the deletion of registry keys under HKEY_CURRENT_USER\Software\Microsoft\Terminal Server Client\Servers\, which store records of previously connected remote systems via Remote Desktop Protocol (RDP). These keys are created automatically when a user connects to a remote host using the native Windows RDP client (mstsc.exe) and can be valuable forensic artifacts for tracking remote access activity. Malicious actors aware of this behavior may delete these keys after using RDP to hide evidence of their activity and avoid detection during incident response. This form of artifact cleanup is a known defense evasion technique, often performed during or after lateral movement. Legitimate users rarely delete these keys manually, making such actions highly suspicious—especially when correlated with RDP usage, unusual logon behavior, or other signs of compromise. Detecting the deletion of these registry entries can provide crucial insight into attempts to cover tracks following interactive remote access.
This detection identifies the deletion of files within the AutomaticDestinations folder, located under a user’s AppData\Roaming\Microsoft\Windows\Recent directory. These files are part of the Windows Jump List feature, which records recently accessed files and folders tied to specific applications. Each .automaticDestinations-ms file corresponds to a program (e.g., Explorer, Word, Notepad) and can be valuable for forensic analysis of user activity. Adversaries may target this folder to erase evidence of their actions, such as which documents or directories were accessed during a session. This type of deletion is rarely seen during normal user activity and may indicate deliberate anti-forensic behavior. When correlated with suspicious logon events, RDP usage, or script execution, this activity may represent an attempt to cover tracks after data access, lateral movement, or staging for exfiltration. Detecting removal of these artifacts can highlight post-compromise cleanup efforts and help analysts reconstruct attacker behavior.
This detection identifies the deletion of RDP bitmap cache files—specifically .bmc and .bin files—typically stored in the user profile under the Terminal Server Client\Cache directory. These files are created by the native Windows Remote Desktop Client (mstsc.exe) and store graphical elements from remote sessions to improve performance. Deleting these files may indicate an attempt to remove forensic evidence of RDP usage. While rare in legitimate user behavior, this action is commonly associated with defense evasion techniques used by attackers or red teamers who wish to hide traces of interactive remote access. When observed in conjunction with recent logon activity, RDP session indicators, or script execution, this behavior should be treated as potentially malicious. Monitoring for deletion of these files provides valuable visibility into anti-forensic actions that often follow lateral movement or hands-on-keyboard activity.
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