Microsoft will release just two security updates next week to patch three vulnerabilities in Windows.
One of the two was tagged with the 'critical' label, Microsoft's highest threat ranking, while the other was marked 'important'. Microsoft typically assigns a critical rating to vulnerabilities that can be exploited with little or no action on the part of a user.
Both updates will patch flaws in Windows.
What Microsoft pegged as 'Bulletin 1' in the advance notification it published will affect only Windows Vista, while 'Bulletin 2' will affect all still-supported versions of the OS, with the client editions - XP, Vista and Windows 7 - labelled critical and the server software rated important.
"The Vista one is confusing," said Andrew Storms, director of security operations at nCircle Security. "It's either something introduced in Vista but doesn't exist in Windows 7, or the component was rewritten for Windows 7."
Storms speculated that the flaw might be in a part of operating system that's little used, such as the task scheduler.
As for Bulletin 2, Microsoft's bare bones write-up - typical of its advance warnings prior to Patch Tuesday - also doesn't offer many clues.
"It's critical in all the desktop clients and important in the server, and consistent in the whole stack," said Storms, talking about Microsoft's threat ratings. "The difference in the criticality is confusing, and Microsoft's not giving us much to go on."
The bug(s) patched by Bulletin 2 are most likely in an operating system DLL (dynamic-link library), said Storms, perhaps a driver or database connector, that's crucial to the OS.
Next week's updates will be a far cry from last month's, when Microsoft issued a record 17 security bulletins and fixed 40 flaws, the second-largest number ever.
"I'll take it," said Storms, referring to the relatively easy Patch Tuesday next week compared to the monster update Microsoft pushed to customers in December.
Microsoft will not be patching either of the vulnerabilities that the company recently acknowledged - and issued security advisories for - said Carlene Chmaj, a spokeswoman for the Microsoft Security Response Center (MSRC), in a blog . "We continue to actively monitor both vulnerabilities," she said.
Two weeks ago, Microsoft confirmed a critical bug in all versions of IE, including the newest production edition IE8, that hackers could exploit by convincing users to visit a malicious site. The this week, the company acknowledged a serious flaw in Windows XP, Vista, Server 2003 and Server 2008.
Chmaj also confirmed that Microsoft has seen in-the-wild targeted attacks exploiting the IE bug. Microsoft typically releases an emergency, or 'out-of-band', security update only if attacks spike.
Nonetheless, some researchers were surprised that Microsoft isn't addressing the two bugs next week.
"The big shock this month is that Microsoft is not addressing two security advisories that have already been weaponized," Josh Abraham, a researcher with Rapid7.
Storms wasn't so stunned.
"The only chance that they would have patched [the two outstanding bugs] is if they already knew about them months before," Storms said. "If anyone is surprised that [those bugs] are not being patched, they don't follow Microsoft's release cycles very closely."
It's possible, Storms admitted, that Microsoft may be forced to release an IE update a week or two early. That update, expected February 8, would conceivably include not only a fix for the bug Microsoft confirmed December 22, but also one for the vulnerability Google security engineer Michal Zalewski told Microsoft about last July.
"They probably have the first on the schedule for February already," said Storms.
Abraham anticipates an early IE update. "I would bet that if the malicious attackers start using the [public] exploits then we will see an out-of-band patch," he said.
See also: Microsoft warns of Word attacks