DNS Server Vulnerability CVE-2020-1350

Before you modify it, back up the registry for restoration in case problems occur.

To work around this vulnerability, make the following registry change to restrict the size of the largest inbound TCP-based DNS response packet that’s allowed:

Subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DNS\Parameters 

Value: TcpReceivePacketSize

Type: DWORD 

Value data: 0xFF00

Notes

  • The default (also maximum) Value data = 0xFFFF.
  • The recommended Value data = 0xFF00 (255 bytes less than the maximum).
  • You must restart the DNS Service for the registry change to take effect. To do this, run the following command at an elevated command prompt:

net stop dns && net start dns

After the workaround is implemented, a Windows DNS server will be unable to resolve DNS names for its clients if the DNS response from the upstream server is larger than 65,280 bytes.

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