Mitigate A New CERT Vulnerability (#598349) With An Entry In /etc/hosts

There is a new CERT vulnerability that can leave you vulnerable to a Man-in-the-Middle attack. You can mitigate this vulnerability today by adding these two lines to your /etc/hosts file:

0.0.0.0 wpad wpad.example.com 
:: wpad wpad.example.com

example.com is a stand in for your local domain. So replace example.com with whatever your local domain is.

The essence of this vulnerability is that an attacker can add a device to the network named wpad and get a DHCP lease, thus inserting the name wpad.example.com in the local DNS pointing to the attacker’s machine. The presence of that A record allows control of the proxy settings of any browser in the network.

You can learn more about the technology behind this attack at Google’s Project Zero page–it’s an older article, but gives some insight into the inner workings of the attack.

The next release of dnsmasq includes an option (dhcp-ignore-names) that can be used to mitigate the attack at the source, but we haven’t heard how Simon will act on this new vulnerability.

Since FTLDNS is just our fork of dnsmasq, we can easily merge in any upstream changes from him, but we wanted to let you know of the /etc/hosts fix that you can immediately implement.