• A host rapidly makes use of multiple accounts via the SMB protocol which can be used for file sharing, RPC and other activity

Possible Root Causes

  • An attacker is trying to determine the existence of accounts in order to progress to the next step in the attack
  • The attacker is working through a list of accounts with well-known default passwords in an attempt to find a working account/password combination
  • This host provides services through a portal and many users are using the portal by logging in and requesting services which require an SMB connection to fulfill

Business Impact

  • An account scan is an effective way for an attacker to determine what accounts are available inside an organization’s network
  • Reconnaissance within a network is a precursor to active attacks which ultimately exposes an organization to substantial risk of data acquisition and exfiltration
  • This form of reconnaissance is often a lot less noticeable than a port sweep or a port scan so attackers feel they can use it with relatively little risk of detection

Steps to Verify

  • If logs of user session activity are available, examine the logs for a more detailed view of activity by this host
  • Inquire whether the host should be utilizing the user accounts listed in the detection
  • Verify that the host from which authentication is attempted is not a shared resource as this could generate a sufficient variety of account usage to resemble an account scan


What exactly is SMB scanning and why is it significant?

SMB scanning involves probing a network for open SMB ports or identifying active SMB services. It's significant because it can indicate either legitimate administrative activities or malicious reconnaissance efforts.

How does SMB scanning differ when done for legitimate vs. malicious purposes?

Legitimate SMB scanning is conducted by network administrators for managing resources or ensuring authorized SMB services. Malicious SMB scanning is performed by attackers to find entry points into a network or exploit vulnerabilities.

What are some common signs of an SMB account scan?

Signs include rapid account access attempts, login attempts from multiple IP addresses, unusual activity times, access to multiple resources, high traffic volume, use of common credentials, security tool alerts, repeated account lockouts, and geographic irregularities.

Why do attackers perform SMB account scans?

Attackers scan SMB accounts for credential harvesting, identifying vulnerabilities, network mapping, lateral movement within a network, installing malware, data exfiltration, and service disruption.

What are the business implications of an SMB account scan?

Implications include security breaches, operational disruption, ransomware/malware attacks, resource drain, compliance and legal issues, reputational damage, intellectual property theft, and financial losses.

What are some investigative measures to address SMB account scans?

Measures include analyzing logs, verifying account usage, and assessing if the scanning host is a shared resource that might mimic scanning activity.

How can SMB scanning lead to lateral movement within a network?

Once inside a network, attackers use SMB scanning to locate other vulnerable systems or accounts, allowing them to spread the attack and gain deeper access.

How does SMB scanning facilitate credential harvesting?

Attackers use SMB account scanning to identify valid user credentials through brute-force attacks or credential stuffing.

What role do outdated SMB protocols play in these scans?

Older SMB versions, like SMBv1, have known vulnerabilities that can be easily exploited, making them prime targets in SMB scanning.

How can organizations protect against SMB account scans?

Organizations should regularly update and patch systems, implement strong authentication mechanisms, monitor network traffic, and educate employees about security best practices.

What should be the immediate response upon detecting an SMB account scan?

Immediately investigate the origin and nature of the scan, assess the extent of access or damage, and initiate appropriate security measures to contain and mitigate the threat.