Network Security Group

Open NetBIOS

Risk Level: High

Description: 

This plugin checks whether NetBIOS UDP port 137 or 138 is available to the public. While some ports, like HTTP and HTTPS, must be open to the public in order to function, other sensitive services, like NetBIOS, should be limited to known IP addresses. If the accessibility of the IP addresses is not kept in check it could make the account vulnerable to attacks.

PingSafe strongly recommends restricting UDP ports 137 and 138 to known IP addresses.

About the Service :

In an Azure virtual network, a network security group may be used to restrict network traffic to and from Azure resources. A network security group is a collection of security rules that allow or disallow incoming and outgoing network traffic to and from various Azure services. Source and destination, port, and protocol can all be specified for each rule.

Impact : 

If the ports are unrestricted, they can make the account vulnerable to attacks. This could lead to the accessibility of sensitive data to the people it’s not meant to be accessible by. If we do not restrict UDP ports 137 and 138  to known IP addresses the best security practices will not be followed and attacks can be invoked.

Steps to reproduce :

  1. Sign in to your Azure portal with your Azure account.
    https://portal.azure.com/#home 
  2. Navigate to Azure’s Network Security Groups.
  3. Click on the Security Group that you want to examine. Next, click on the inbound security rules.
  4. Check whether UDP ports 137 and 138 are showing Allow for all Source and Destination. If it shows Allow that means it is exposed to the public.
  5. Follow the same steps for other security groups as well.

To check if UDP ports 137 and 138 are accessible to the general public or not we examined the port Inbound Security Rules.

Steps for remediation :

  1. Sign in to your Azure portal with your Azure account.
    https://portal.azure.com/#home 
  2. Navigate to Azure’s Network Security Groups.
  3. Click on the Security Group that you want to examine. Next, click on the inbound security rules.
  4. Check whether UDP ports 137 and 138  are showing Allow for all Source and Destination. If it shows Allow that means it is exposed to the public.
  5. Next, click on the security group rule and change the source port and click Save.
  6. Now the UDP ports 137 and 138  are not accessible by the public.
  7. Follow the same steps for other security groups as well.

References :

Please feel free to reach out to support@pingsafe.ai with any questions that you may have.

Thanks

PingSafe Support