For the second time in three days, Microsoft added another product to the list of those vulnerable to a critical bug patched nearly three weeks ago.
Windows Home Server, the company's newest operating system, is also at risk to the vulnerabilities spelled out by the MS08-001 security bulletin, according to a Friday update. The advisory, first issued on January 8 -- and then fingered by researchers as the month's most pressing -- was revised Wednesday, when Microsoft announced that Windows Small Business Server was at risk. Neither Windows Home Server or Small Business Server had been among the versions mentioned in the original bulletin.
"Supported editions of Windows Small Business Server 2003 and Windows Home Server contain the same affected code as Windows Server 2003," Microsoft said in the revised notice. "[However], Windows Small Business Server and Windows Home Server configurations have IGMP [Internet Group Management Protocol] enabled by default and will result in a greater exposure to the same vulnerability."
The initial bulletin had pegged the threat to Windows Server 2003 as "important," the second highest rating in Microsoft's four-step scoring system. But it was later rated as "critical" for Windows Home Server and Small Business Server.
According to Microsoft, the vulnerability can be exploited by sending malicious data packets to unsuspecting users, who could find their PCs infected with malware or under the control of others. Within 10 days of Microsoft posting its first patches, researchers had produced proof-of-concept exploits, claiming that the company had overestimated the difficulty in crafting attack code.
"It's apparently possible to create a reliable exploit for this issue," noted Symantec on Jan. 18.
Windows Home Server owners have been offered the patch via the software's update mechanism, Microsoft said in the revised bulletin. "Customers should apply the update to remain secure," it urged.
Microsoft did not say why it had not identified Windows Home Server or Small Business Server as vulnerable and requiring repair when it first issued updates earlier this month.