Open NetBIOS

Quick Info

Plugin TitleOpen NetBIOS
DescriptionDetermine if UDP port 137 or 138 for NetBIOS is open to the public
More InfoWhile some ports such as HTTP and HTTPS are required to be open to the public to function properly, more sensitive services such as NetBIOS should be restricted to known IP addresses.
AWS Link
Recommended ActionRestrict UDP ports 137 and 138 to known IP addresses

Detailed Remediation Steps

  1. Log into the AWS Management Console.
  2. Select the “Services” option and search for EC2.
  3. Scroll down the left navigation panel and choose “Security Group” under “Network & Security”.
  4. Select the “EC2 Security Group” that needs to be verified.
  5. Scroll down the bottom panel and choose “Inbound”. Verify the value for “Source” column for “Custom UDP Rule” under “Type” for port “137 or 138” and if any rule have value set to “” or “::/0 " then the selected “Security Group” has “UDP” port for “NetBIOS” open to the public.
  6. Repeat steps number 2 - 5 to verify other “Security Groups” in the selected AWS region.
  7. Navigate to “Security Groups” under “Network & Security” and select the “Security Group” that needs to modify to restrict the access of “UDP” port “137 or 138” for “NetBIOS” to specific ip address.
  8. Scroll down the page and select the “Inbound” and click on the “Edit” button.
  9. In the “Edit inbound rules” tab select either the “MyIP” or “Custom” from the “Source” column.
  10. In the “Edit inbound rules” tab select the “MyIP” from the “Source” column to allow “NetBIOS” inbound traffic only from specific IP address. <img src="/resources/aws/ec2/open-netbios/step10.png)
  11. In the “Edit inbound rules” tab select the “Custom” from the “Source” column as per the requirements for “NetBIOS” and specify static IP/Elastic IP address along with “Description” for the “Security Group” rule. <img src="/resources/aws/ec2/open-netbios/step11.png)
  12. Click on the “Save” button to make the necessary changes. <img src="/resources/aws/ec2/open-netbios/step12.png)
  13. Repeat steps number 7 - 12 to restrict UDP port 445 for “CIFS” to known IP address.