Microsoft has released a patch it says eliminates the vulnerability in Office 2000 and component applications such as Word 2000, Excel 2000 and PowerPoint 2000.
The flaw was revealed by the security firm @Stake. L0pht Research Labs, which said the problem originated with an ActiveX control named Microsoft Office UA Control that shipped with Microsoft Office 2000. According to Microsoft, the Office 2000 UA Control, which is installed by default, is used by the "Show Me" function in Office Help to allow Office functions to be scripted.
While the control is categorised as "safe for scripting," @Stake's analysis of the control's interface showed that it could script almost any action into Office 2000 - including the lowering of macro security settings. The @Stake advisory noted that the script can be delivered from any HTML page that is viewed in an application with active scripting enabled, including default configurations of Internet Explorer and the Outlook email client.
"With the vulnerability you could completely take over someone's machines, steal the whole cookie file, steal or modify any file, plant remote-control software, etc," said @Stake security researcher Weld Pond, who noted that the hole was potentially much more damaging than the recently discovered Internet Explorer cookie vulnerability.
Microsoft acknowledged in its Security Bulletin that the Active X control that shipped with Office 2000 is incorrectly marked as "safe for scripting." It confirmed that a malicious website operator could use the flaw to carry out Office functions on the machine of a user who visited the site.
The @Stake researcher who discovered the hole, who goes by the name DilDog, was thanked by Microsoft in a security bulletin that acknowledged the flaw.
DilDog also noted in the advisory that while the control was labeled "safe for scripting" and assessable remotely, it was undocumented by Microsoft.
Microsoft was not available for comment by press time, but Pond said the company responded swiftly.
"Microsoft took the problem very seriously and fixed the problem in record time," said Pond.
@Stake posted a demonstration of the vulnerability on its website, which sets Word 2000 macro security settings to "low" and then presents an option to set them back to "high" or "medium." While DilDog says the demonstration is written to be harmless, he noted in the advisory that it could easily include more malicious code that could modify files, propagate worms and viruses, or give attackers external access to internal network resources.
"The fact that this control exists and is installed in this particular fashion would permit the construction of a worm of unparalleled devastation, as it would be able to turn off macro virus protection and 'script' its way to all of the people in your address book," DilDog in the @Stake advisory.
Microsoft asserted that its patch removed all unsafe functionality and disables the "Show Me" function in Office 2000.