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Reconnaissance

Outbound Port Sweep

Outbound Port Sweep
Overview
Possible Root Causes
Example Scenarios
Business Impact
Steps to Investigate
MITRE ATT&CK Techniques
Related Detections
FAQ

Detection overview

An Outbound Port Sweep detection indicates that an internal host is scanning multiple ports on external hosts. This behavior is often associated with compromised internal machines attempting to identify open and vulnerable services on the internet. Detecting outbound port sweeps is crucial as it helps in identifying compromised hosts within the network that may be part of a larger attack campaign or botnet.

Triggers

  • An internal host is generating many more unsuccessful attempts to connect to external services than successful ones

Possible Root Causes

  • An internal host is part of a botnet and is being used by its bot herder to find other external services that could subsequently be attacked
  • An internal host is misconfigured and is making many connection attempts to different IP addresses on the Internet

Business Impact

  • Botnet activity presents several risks to the organization: (1) it creates noise which may hide more serious issues; (2) there is a chance your organization’s IP will end up on black lists; and (3) the compromised host can always be instructed to perform a direct attack on the organization
  • A misconfigured internal host may be using unnecessary bandwidth and slowing down both the host itself and other applications as a result of the traffic it is sending

Steps to Investigate

  • Look at the pattern of IP addresses being scanned to determine the intent of the scan
  • Verify whether there is misconfigured software on the host which is causing the scan
  • If the behavior cannot be explained by user action or known software behavior, the host is likely infected and should be remediated
Outbound Port Sweep

Possible root causes

Malicious Detection

  • A compromised internal host used by an attacker to perform reconnaissance on external networks.
  • Malware or botnets installed on an internal machine conducting port scans to identify external vulnerabilities.
  • Insider threat where an internal user deliberately performs unauthorized port scanning.

Benign Detection

  • Network security tools conducting external vulnerability assessments as part of regular security practices.
  • Misconfigured software or scripts unintentionally generating outbound port scan traffic.
  • Routine administrative tasks that involve querying multiple external services.
Outbound Port Sweep

Example scenarios

Scenario 1: An internal host starts sending a high number of SYN packets to various ports on external IP addresses. Upon investigation, it is found that the host is infected with malware, and the attacker is using it to scan for vulnerable services on the internet.

Scenario 2: A sudden spike in outbound port scanning activity is detected. Further analysis reveals that a network security team was performing an authorized external vulnerability assessment without prior notification, leading to the detection trigger.

Outbound Port Sweep

Business impact

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

Network Reputation Damage

Outbound port sweeps from an organization's network can lead to IP blacklisting, impacting the organization's ability to communicate with external services.

Identification of Compromised Hosts

Detection helps in identifying compromised internal machines, allowing for timely remediation to prevent further malicious activities.

Potential Regulatory Issues

Uncontrolled outbound scanning activity may violate industry regulations or security policies, leading to compliance issues.

Outbound Port Sweep

Steps to investigate

Analyze Firewall and IDS/IPS Logs

Review logs to identify the source of the outbound port sweep and the targeted external IP addresses and ports.

Check the Host Configuration

Investigate the internal host generating the traffic to determine if it is compromised or misconfigured.

Correlate with Other Security Events

Look for other signs of compromise, such as malware alerts, unusual login attempts, or data exfiltration activities.

Verify with Network and Security Teams

Confirm if the activity is part of any authorized security assessments or administrative tasks.

Outbound Port Sweep

MITRE ATT&CK techniques covered

Remote System Discovery

T1018

Network Service Discovery

T1046

Network Sniffing

T1040
Outbound Port Sweep

Related detections

Kerberos Brute-Sweep

Suspicious Port Sweep

Kerberoasting: SPN Sweep

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FAQs

What is an Outbound Port Sweep?

An Outbound Port Sweep involves an internal host scanning multiple ports on external hosts to identify open and potentially vulnerable services. This activity is often associated with compromised hosts attempting to map external networks.

What are the common signs of an Outbound Port Sweep?

Common signs include multiple connection attempts to various external ports, high volumes of incomplete connection attempts (SYN packets without SYN-ACK responses), and unusual outbound traffic patterns.

Can legitimate software trigger this detection?

Yes, network security tools, misconfigured software, or routine administrative tasks can generate outbound port sweeps that may trigger this detection.

How does Vectra AI identify Outbound Port Sweeps?

Vectra AI uses advanced AI algorithms and machine learning to analyze outbound network traffic patterns and identify anomalies indicative of port sweeping activities.

What is the business impact of an Outbound Port Sweep?

It can lead to network reputation damage, identification of compromised hosts, and potential regulatory issues due to uncontrolled outbound scanning activities.

How can I detect an Outbound Port Sweep in my network?

Detect Outbound Port Sweeps by monitoring for high volumes of outbound SYN packets, connection attempts to multiple external ports, and deviations from normal network traffic patterns.

Why are Outbound Port Sweeps a significant threat?

They can indicate compromised internal hosts being used for malicious reconnaissance, potentially leading to IP blacklisting, identification of vulnerable external services, and further malicious activities.

What steps should I take if I detect an Outbound Port Sweep?

Investigate the source and scope of the scanning activity, check for associated suspicious activities, review logs, and consult with network and security teams to verify if the activity is legitimate.

What tools can help verify the presence of an Outbound Port Sweep?

Tools such as firewall and IDS/IPS logs, network traffic analysis tools, and SIEM solutions can help verify and investigate suspicious outbound port sweep activities.

How can I prevent Outbound Port Sweeps?

Implement robust network monitoring and alerting, enforce strict access controls, regularly conduct security assessments, and ensure timely patching and updating of services to minimize vulnerabilities.