An unpatched bug in a file installed with Microsoft's Office and Visual Studio software could lead to some serious problems for Internet Explorer users, security researchers have reported.
An attacker could seize control of a vulnerable system by exploiting the bug, which the FrSIRT (French Security Incident Response Team) reported in an alert published Wednesday. This would be achieved by installing malicious code in a Web page that exploits a memory corruption error in a file that ships with Microsoft Office 2002 and Microsoft Visual Studio .Net 2002 products, the research organisation said.
Though the attack would be executed via the popular Internet Explorer (IE) browser, only systems that contain the file in question, called Msdds.dll, are vulnerable, FrSIRT said. The FrSIRT said it has not yet seen a patch for the vulnerability.
Msdds.dll is software that is used for creating customised Office applications, according to Russ Cooper, senior information security analyst for Cybertrust.
Cooper does not believe that this file has been installed on a large number of Windows systems. "I'm not concerned about it," he said via instant message. "I don't doubt it is shipped with the full Office Professional installation CD, but I highly doubt it is installed automatically."
Neither Microsoft nor FrSIRT could say whether this file was installed by default with Office or Visual Studio.
Microsoft has yet to see any attackers taking advantage of the flaw, a Microsoft spokeswoman said Thursday. But reports are circulating of Web sites that take advantage of another Internet Explorer bug, which Microsoft patched on Aug. 9.
About a dozen Web sites have cropped up that take advantage of a flaw in IE's JPEG rendering engine, according to Dan Hubbard, senior director of security and research with Websense. If unpatched IE users go to these Web sites, their systems could be made to crash, or they could be made to run software that allows an attacker to gain control of the system, he said.
Because users must first be tricked into clicking on the malicious Web site for the attack to work, this exploit is not considered as dangerous as the recent round of Windows Plug and Play worms that were widely reported earlier this week.
But attackers are increasingly using Internet Explorer rather than e-mail viruses as a way of seizing control of systems, Hubbard said. "In the last year we've seen a huge trend toward malicious Web sites being used as an attack vector," he said. "E-mail is just not as effective as it used to be."
The Microsoft spokeswoman would not say whether or not a patch is planned for the Msdds.dll bug, but on Thursday the company published a security advisory discussing the problem. The advisory, which includes a number of suggested work-arounds, can be found here: http://www.microsoft.com/technet/security/advisory/906267.mspx .
The FrSIRT alert can be found here: http://www.frsirt.com/english/advisories/2005/1450 .
A SANS Institute alert with instructions on how to check for the Msdds.dll file can be found here: http://isc.sans.org/diary.php?date=2005-08-18