Security experts are warning Microsoft customers about silent Internet attacks that exploit a security flaw in the Internet Explorer Web browser, potentially allowing remote attackers to run malicious code on vulnerable machines.
The vulnerability is similar in scope to those exploited by devastating worms such as Nimda, Badtrans and Klez, according to one security company. And, to make matters worse, the flaw is one Microsoft said it fixed weeks ago.
The security hole, known as the "Object Data vulnerability," affects Internet Explorer (IE) versions 5.01, 5.5 and 6.0. It concerns the way that IE processes HTML (Hypertext Markup Language) pages containing a special element called the Object Data tag. If properly exploited, the vulnerability could enable an attacker to place a malicious computer program on a user's machine. No user actions would be required aside from opening an e-mail message or visiting a Web page containing the attack.
On August 20, Microsoft released a patch for IE, MS03--032, that it said closed the hole, in addition to patching other security holes in IE.
According to a message posted to a prominent security discussion group Sunday, however, the vulnerability still exists on machines using IE even after applying the patch.
A Microsoft spokesman confirmed that the company is investigating the reports of new exploits for one of the vulnerabilities addressed in the MS03-032 security bulletin.
However, Microsoft still recommends that customers install that patch, he said.
The software company is not aware of any customers who have been attacked using the vulnerability, he said.
However, security researchers know of at least one exploitation of the Object Data vulnerability that is already circulating on the Internet, according to a statement by security company Secunia of Copenhagen, Denmark.
An e-mail message that contains HTML code that exploits the vulnerability is used to silently retrieve and run a file, "drg.exe," that installs a file called "surferbar.dll" onto the victim's computer, according to the Secunia alert.
That file adds a new bar to the affected users' Internet Explorer Web browser with links to pornographic Web sites, the company said.
The Object Data vulnerability is also similar to an earlier IE security hole dating to 2001, MS01-020, that was exploited by virulent e-mail worms such as Nimda and Klez, according to Secunia.
Security experts familiar with the issue say that Microsoft's failure to thoroughly test their patch against attack scenarios using the Object Data vulnerability is a black eye for the company.
"Microsoft should be ashamed. This is a major embarrassment," said Richard Smith, an independent security analyst based in Boston.
The problem with the Object Data vulnerability is similar to a hole found in a prior Microsoft patch, according to Israeli security company GreyMagic Software, which issued a report on the problem in Feb. 2002.
That fact points to problems with Microsoft's patch testing process, Smith said.
"They need to go back and look at how this slip-up occurred. They keep saying they can't prevent bugs, but when the same problems keep occurring over and over, that's a management issue," he said.
A Microsoft spokesman said the company is committed to keeping customers data safe and will take "appropriate action" to protect customers when its investigation into the new exploits is complete.
In the absence of a patch from Microsoft to fix the problem, security experts recommended disabling support for Active Scripting on affected IE versions. Failing that, users should consider uninstalling the popular browser to protect themselves from attack, experts said.