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SMB Brute-Force

SMB Brute-Force
Overview
Possible Root Causes
Example Scenarios
Business Impact
Steps to Investigate
MITRE ATT&CK Techniques
Related Detections
FAQ

Detection overview

The "SMB Brute-Force" detection focuses on identifying attempts to gain unauthorized access to systems by brute-forcing credentials over the Server Message Block (SMB) protocol. SMB is widely used for network file sharing and resource access in Windows environments. Attackers often target SMB to obtain valid credentials, which can be used to move laterally within the network, escalate privileges, and access sensitive data.

The SMB (Server Message Block) Brute-Force detection is designed to identify and alert on potential malicious activities aimed at exploiting SMB services through repeated password guessing attempts.

Triggering Behavior: Excessive Authentication Attempts

SMB Brute-force detection is triggered by an internal host rapidly utilizing multiple accounts through the SMB protocol, notably for activities that involve file sharing or RPC.

This behavior is indicative of an attempt to ascertain the existence of accounts, potentially followed by password brute-forcing using common or default passwords.

Underlying Reasons for SMB Brute-force

This behavior may be caused by attackers trying to uncover usable account credentials within a network. These accounts can then be used to escalate privileges or move laterally within the system.

Alternatively, it could be a benign scenario where a host provides services through a portal, leading to multiple users logging in for services requiring an SMB connection.

Business Impact of SMB Brute-force

The primary risk from SMB brute-force attacks is the unauthorized discovery and exploitation of internal accounts, posing significant threats to data security and network integrity.

Such reconnaissance is often the precursor to more severe attacks, potentially leading to substantial data breaches or system disruptions.

Steps to Verify

To effectively investigate an SMB Brute-Force alert, follow these steps:

  1. Determine whether the internal host in question should be connecting to the target host using the indicated account(s); if not, this is likely malicious behavior
  2. Determine which process on the internal host is initiating the SMB requests; in Windows systems, this can be done using a combination of netstat and tasklist commands
  3. Verify that the process should be running on the internal host and whether the process is configured correctly
SMB Brute-Force

Possible root causes

Malicious Detection

  • An attacker is using automated tools to brute-force SMB credentials to gain unauthorized access.
  • Compromised systems within the network are being used to perform SMB brute-force attacks.
  • Insider threat where an employee is attempting to access restricted SMB resources by brute-forcing credentials.

Benign Detection

  • Legitimate users repeatedly trying to log in after forgetting their passwords.
  • Security assessments or penetration tests involving controlled brute-force attack simulations.
  • Misconfigured applications or systems causing repeated login attempts.
SMB Brute-Force

Example scenarios

Scenario 1: An attacker from an external IP address uses an automated tool to perform a brute-force attack on a company's SMB services, trying multiple usernames and common passwords. The detection is triggered by the high volume of failed login attempts from a single IP address.

Scenario 2: During a penetration test, the security team runs a controlled brute-force attack simulation on the organization's SMB services. The detection is triggered, and the activity is verified as part of the scheduled assessment.

SMB Brute-Force

Business impact

If this detection indicates a genuine threat, the organization faces significant risks:

Credential Compromise

Successful brute-force attacks can lead to unauthorized access to systems and sensitive data.

Lateral Movement

Attackers can use compromised credentials to move laterally within the network, escalating privileges.

Operational Disruption

Brute-force attacks can overwhelm authentication services, causing performance degradation and potential outages.

SMB Brute-Force

Steps to investigate

Review Authentication Logs

  • Check logs for patterns of multiple failed login attempts to SMB services, including timestamps, source IP addresses, and usernames.
  • Identify any successful login attempts following a series of failures.

Correlate with User Activity

  • Verify if the affected accounts are associated with legitimate users who may have forgotten their passwords.
  • Check for recent changes in user behavior, access patterns, or account privileges.

Examine Network Traffic

  • Analyze network traffic for unusual patterns or spikes in SMB activity.
  • Look for connections to known or suspicious IP addresses involved in brute-force attempts.

Conduct a Threat Hunt

  • Search for other indicators of compromise or malicious activity associated with the same IP addresses or user accounts.
  • Verify if the detected activity is part of a scheduled security assessment or penetration test.
SMB Brute-Force

MITRE ATT&CK techniques covered

Brute Force

T1110

Account Discovery

T1087
SMB Brute-Force

Related detections

Brute-Force

Azure AD Successful Brute-Force

Kerberos Brute-Sweep

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FAQs

What is an SMB brute-force attack?

An SMB brute-force attack involves repeatedly attempting to guess the correct username and password for accessing SMB services, often using automated tools, until successful authentication is achieved.

What are the common signs of an SMB brute-force attack?

Common signs include multiple failed login attempts from a single IP address, unusual patterns of authentication attempts, sudden spikes in SMB traffic, and alerts from IDS/IPS.

Can legitimate activities trigger the detection of SMB brute-force attacks?

Yes, legitimate users forgetting their passwords, security assessments, or misconfigured applications can trigger this detection. It’s important to verify the context of the activity.

How does Vectra AI detect SMB brute-force attacks?

Vectra AI uses advanced AI algorithms to analyze authentication logs and network traffic, identifying patterns indicative of brute-force attacks and correlating these with other suspicious behaviors.

What is the business impact of an SMB brute-force attack?

The primary risks are credential compromise, unauthorized access, lateral movement, data breaches, and operational disruptions, which can lead to significant harm to the organization.

How can I detect SMB brute-force attacks in my environment?

Monitor authentication logs for multiple failed login attempts, analyze network traffic for unusual SMB activity, and set up alerts for spikes in authentication failures.

Why is an SMB brute-force attack a significant threat?

Successful brute-force attacks can lead to credential compromise, unauthorized access to systems and sensitive data, lateral movement within the network, and potential data breaches.

What steps should I take if I detect an SMB brute-force attack?

Investigate the source of the login attempts, verify if they are legitimate, check for other signs of malicious activity, and take steps to secure affected accounts and systems.

What tools can help verify the presence of SMB brute-force attacks?

Tools like authentication log analyzers, security information and event management (SIEM) systems, and specialized monitoring solutions can help identify and verify SMB brute-force attacks.

How can I prevent SMB brute-force attacks?

Implement strong password policies, use multi-factor authentication (MFA), monitor authentication logs, set up account lockout mechanisms, and regularly audit user activity and access controls.