A security analyst is investigating a series of alerts from a SIEM indicating 'High Volume of Outbound SMB Traffic' from an internal file server to numerous internal workstations, occurring outside business hours. Further investigation reveals that the file server is not typically used to initiate SMB connections to workstations, but rather to serve files. What is the most likely cause of this activity?
- AWorm or ransomware propagation
- BInsider threat for data exfiltration
- CLegitimate software update deployment
- DBackup process misconfiguration
Show answer & explanationAnswer & explanation
Correct answer: A. Worm or ransomware propagation
SMB (Server Message Block) is a common protocol used for file sharing on Windows networks. A 'high volume of outbound SMB traffic' from a file server (which usually acts as a *receiver* of SMB connections from clients, not an *initiator* to many workstations) to 'numerous internal workstations' outside business hours is a strong indicator of lateral movement by malware, especially worms or ransomware. These threats often exploit SMB vulnerabilities or stolen credentials to spread rapidly across a network.
Why the other options are wrong
- B. Insider threat for data exfiltration would typically involve data moving *out* of the network or from workstations to external storage, not high-volume SMB from a file server *to* internal workstations.
- C. Software updates are typically deployed from a central management server (e.g., WSUS, SCCM), not usually initiated as high-volume SMB from a file server to many workstations.
- D. Backup processes typically involve data transfer from workstations *to* the file server or from the file server to dedicated backup storage, not high-volume SMB initiated from the file server to many workstations.
Lateral Movement via SMB
A common technique used by attackers and malware (especially worms and ransomware) to spread from one compromised system to other systems within the same network, often leveraging SMB (Server Message Block) for file sharing and remote execution.
- Relies on SMB vulnerabilities or weak/reused credentials.
- Often seen as unusual outbound SMB from a compromised host.
- Enables rapid propagation across Windows environments.
Memory trick: Malware spreads like a virus, finding new hosts to infect.