Ensure that Microsoft Azure network security groups (NSGs) do not allow unrestricted access on TCP and UDP port 53 in order to protect against attackers that use brute force methods to gain access to Azure virtual machines associated with these NSGs. TCP/UDP port 53 is used by the Domain Name Service during DNS resolution (DNS lookup), when the requests are sent from DNS clients to DNS servers or between DNS servers.
This rule resolution is part of the Conformity Security & Compliance tool for Azure.
Allowing unrestricted access to your Azure virtual machines (VMs) via network security groups (NSGs) can increase opportunities for malicious activities such as Denial of Service (DoS) attacks or Distributed Denial of Service (DDoS) attacks.
Audit
To determine if your Azure network security groups allow unrestricted access on TCP and UDP port 53, perform the following actions:
Remediation / Resolution
To update your Azure NSG rule(s) configuration in order to restrict DNS access to trusted entities only, such as admin IP addresses or IP ranges, perform the following actions:
References
- Azure Official Documentation
- Azure network security overview
- Network security groups
- Create, change, or delete a network security group
- Azure best practices for network security
- Azure PowerShell Documentation
- az mysql server
- az network nsg list
- az network nsg rule list
- az network nsg rule update
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Check for Unrestricted DNS Access
Risk Level: High