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Hidden custom DNS settings on windows

When two static DNS addresses are set by the user via the control panel or the netsh command, they are stored in the registry as a list where each entry is separated by a comma (e.g. 192.168.1.21,192.168.1.22). Static DNS addresses can be manually added in the registry, but the modification is not shown in the control panel if the comma is replaced by a space (e.g. 192.168.1.21 192.168.1.22). If the ipconfig /all command is used to check the network settings, the static DNS address is displayed, but users are informed that the address is obtained automatically.

 

Adding the DNS addresses manually to the registry with a space between them allows attackers to hijack DNS settings without leaving an apparent trace. ESET pointed out that this could be a major problem for regular users and companies that offer remote support.

 

There is another method that can be used to identify and remove the rogue DNS addresses besides accessing the registry directly. In the IPv4 properties window, in the advanced settings section, the DNS server addresses are listed next to each other separated by a space, just like in the registry, but they should normally be listed one under another. Users can remove the rogue entries from this menu and their DNS server’s address will once again be obtained automatically.