Microsoft to Change IE Behavior to Block Spoofing Attacks

By Larry Seltzer  |  Posted 2004-01-29 Print this article Print

http://username:password@server/file.html syntax to be disallowed by an upcoming software update. Problematic feature was recently made more dangerous by the unveiling of a display bug in browser.

Microsoft Corp. has announced in a support document that it will be releasing a software update to Internet Explorer and Windows Explorer to disable the use of certain syntax in HTTP URLs. The syntax, designed to allow a username and password to be passed to a password-protected page, has a history of abuse. The company did not give a timeline for the release of the patch. The syntax takes the form http[s]://username:password@server/file.html, such as, where "joe" is the username and "blow" is the password. But a site that does not look for the username and password will ignore the values passed, and only the string after the "@" symbol is used for the domain name. Other browsers support this syntax to varying degrees.

Because the values before "@" are ignored, attackers have often attempted to use them to confuse users into believing that they are going to a different site than they are actually visiting. For example, the URL might appear to be going to, but it is actually going to the IP address

The problem was compounded by the recent discovery of a display bug in Internet Explorer that stops the browser from displaying parts of the URL. This allows an attacker utilizing both techniques to display only the legitimate looking portion of the URL to the user.

Microsoft took some time deciding how to address the problem, but on Tuesday released the support document. After installing the patch, Internet Explorer will react to the syntax with a Web page containing the following error message: "Invalid syntax error."

A registry entry will be available for users to re-enable the feature, or to enable it in third-party software that uses the IE Web browser control.

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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