Potential Lateral Tool Transfer via SMB Share

This detection identifies the potential lateral transfer of tools via SMB shares within a Windows environment. The rule focuses on detecting the creation or modification of executable files on network shares, a common tactic used by adversaries to propagate malware, tools, and scripts across compromised systems. This activity can be part of a broader attack campaign where attackers leverage SMB to move laterally and execute malicious payloads on multiple hosts. The rule aims to detect activities described in the MITRE ATT&CK techniques T1021.002 (SMB/Windows Admin Shares) and T1570 (Lateral Tool Transfer). The original rule was created in 2020/11/10 and last updated in 2026/03/19 according to the source. This activity is concerning as it represents a key step in lateral movement, enabling attackers to expand their reach and impact within the network.

Attack Chain

1. An attacker gains initial access to a compromised host within the network.
2. The attacker identifies accessible SMB shares using network reconnaissance tools.
3. The attacker attempts to connect to a target SMB share (port 445) from the compromised host.
4. The attacker copies a malicious executable (e.g., a reverse shell, credential dumping tool, or other malware) to the SMB share using file.Ext.header_bytes : "4d5a*" or by file extension such as exe, dll, or ps1.
5. A user or automated process on another host accesses the SMB share and executes the transferred file.
6. The executed file performs malicious actions, such as establishing a reverse shell, stealing credentials, or installing further malware.
7. The attacker leverages the newly compromised host to further expand their lateral movement within the network.

Impact

A successful lateral tool transfer can lead to widespread compromise within an organization's network. Attackers can use the transferred tools to escalate privileges, harvest credentials, install backdoors, and ultimately achieve their objectives, such as data exfiltration, ransomware deployment, or system disruption. The impact can range from data breaches and financial losses to significant operational downtime and reputational damage.

Recommendation

• Deploy the Sigma rules in this brief to your SIEM to detect potential lateral tool transfer activity via SMB shares.
• Review and restrict write access to network shares to only authorized users and groups.
• Monitor network traffic for unusual SMB activity, such as large file transfers or connections from unexpected hosts.
• Enable Sysmon file creation and network connection logging on Windows endpoints to provide the necessary data for the Sigma rules.
• Investigate any alerts generated by the Sigma rules to determine the scope and impact of the potential compromise.
• Consider adding exceptions to the Sigma rules if legitimate file creation over SMB is expected and noisy in your environment.