Internet Explorer 5.01 through 6 SP1 allows remote attackers to spoof the domain of a URL via a "%01" character before an @ sign in the user@domain portion of the URL, which hides the rest of the URL, including the real site, in the address bar, aka the "Improper URL Canonicalization Vulnerability."
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.