03 February 2004
<a href=http://www.microsoft.com =01 %01 %email@example.com/~cnnurgen/microsoft/downloads/details.html> www.microsoft.com/downloads/</a>
1. This looks like: www.microsoft.com/downloads
2. Notice the use of =01 quoted-printable encoding to insert a non-printable ASCII character SOH (01) inside the URL.
3. Notice the use of % encoding to also insert the non-printable ASCII characters 01 and 00 (the latter being a standard string termination in C designed to fool filters that 'printf' the URL).
5. This appears to take the user to www.microsoft.com/downloads, but actually goes to the site at 188.8.131.52.
6. In Microsoft Internet Explorer both the text highlighted in the URL and the URL shown in the status bar indicate that the URL as on microsoft.com.
7. Mozilla Firebird is also fooled by this trick, it terminates the URL at the SOH character.
Another variant has appeared in phishing emails. The pipe character | can be used in a URL. Under Internet Explorer the URL will not be displayed past the pipe. This can be used to make a subdomain look like a top-level domain. In the following example, borrowed from Netcraft
the link will appear as barclays.co.uk in Internet Explorer, but in fact goes to dvdlinKs.at.