Obscuring the Address

By Larry Seltzer  |  Posted 2003-12-11 Print this article Print

Malicious coders, such as phishers, often will use this technique to obscure the actual address of the site they send you to. For example, they might send you a message that appears to be from Paypal and include a link that looks something like this:
    http://www.paypal.com@ (The IP address I used is illegal for the same reason they use 555 phone numbers on TV shows.)
Notice, the numeric string to the right of the @ mark. This link will not take you to www.paypal.com, but to But most unsophisticated users wont notice the difference. Still, all of this monkey business is perfectly legal (if immoral) under the URI standard.
The latest bug adds a twist: If you put ASCII 00 and 01 characters (designated as %00%01 in the spec.) just prior to the @ character, then Internet Explorer wont display the rest of the URL when the user views the page. In Javascript you must use just the %01 character and also decode the string with the unescape() function..
So what does it actually look like? Try pressing the button below. In the Status bar, the link appears to take you to the White House site, but it actually takes you to the latest column of one of our eWEEK columnists. The actual link was: http://www.whitehouse.gov%01%00@www.eweek.com/article2/0,4149,1407901,00.asp The applications for phishing attacks are pretty self-explanatory. The viewer will think theyre on www.paypal.com, or whatever, but they will actually be who-knows-where. Next page: Mozilla not immune.

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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