Aqua CSPM

Open DNS

Quick Info

Plugin TitleOpen DNS
CloudAWS
CategoryEC2
DescriptionDetermine if TCP or UDP port 53 for DNS 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 DNS should be restricted to known IP addresses.
AWS Linkhttp://docs.aws.amazon.com/AWSEC2/latest/UserGuide/authorizing-access-to-an-instance.html
Recommended ActionRestrict TCP and UDP port 53 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 “DNS(UDP)” or “DNS(TCP)” under “Type” and if any rule have value set to “0.0.0.0/0” or “::/0 " then the selected “Security Group” has “TCP/UDP” port 53 for “DNS” 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 “TCP/UDP” port 53 for “DNS” 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 “TCP/UDP” port 53 inbound traffic only from specific IP address.
  11. In the “Edit inbound rules” tab select the “Custom” from the “Source” column as per the requirements for “TCP/UDP” port 53 for “DNS” and specify static IP/Elastic IP address along with “Description” for the “Security Group” rule.
  12. Click on the “Save” button to make the necessary changes.
  13. Repeat steps number 7 - 12 to restrict “TCP/UDP” port 53 for “DNS” to known IP address.