Microsoft fixes bugs that could make “Swiss cheese” of business networks

Microsoft Corp. today patched three vulnerabilities in the company’s Server Message Block (SMB) file-sharing protocol, including two that could make “Swiss cheese” out of enterprise networks, according to one researcher.

“This is super nasty,” said Eric Schultze, the chief technology officer at Shavlik Technologies LLC, who also called today’s update “super critical” as he sounded the alarm. “Expect to see a worm on this one in the very near future, [because] this is Blaster and Sasser all over again.”

Those two worms, 2003’s Blaster and 2004’s Sasser, wreaked havoc worldwide as they spread to millions of Windows machines.

Of the three bugs outlined in the MS09-001 security bulletin, two were rated “critical,” the most serious ranking in Microsoft’s four-step scoring system, while the third was pegged “moderate.”

The pair identified as critical are extremely dangerous because attackers can exploit them simply by sending malformed data to unpatched machines, according to Schultze.

“These flaws enable an attacker to send evil packets to a Microsoft computer and take any action they desire on that computer [with] no credentials required,” he said. “The only prerequisite for this attack to be successful is a connection from the attacker to the victim over the NetBIOS ports, TCP 139 or TCP 445. By default, most computers have these ports turned on.”

Much the same situation led to Blaster and Sasser, Schultze noted. “More people have blocked those ports, and more personal firewalls block them by default, but they are typically left open in a corporate network.”

Amol Sarwate, manager of Qualys Inc.’s vulnerability lab, agreed. “The ports are always open [in the enterprise], and no user intervention is needed,” he said. “This is nasty.”

Today’s update affects all currently-supported versions of Windows, including Windows 2000, XP, Server 2003, Vista and Server 2008, Microsoft noted. Although the newer editions — Vista and Server 2008 — are immune from one of the two critical vulnerabilities.

The second critical bug — which is also wormable, according to Schultze and Sarwate — is rated as moderate for Vista and Server 2008, because those two operating systems have file-sharing disabled by default.

That, plus other mitigating circumstances, must be why Microsoft gave the three bugs its lowest exploitability index rating, even though two carried critical severity rankings, said Andrew Storms, director of security operations at nCircle Network Security Inc.

Security Inc.

“This might be the first time that Microsoft has labeled a critical vulnerability all the way down to ‘3’ on the exploitability index,” said Storms, talking about Microsoft’s relatively new practice of predicting the likelihood of attackers coming up with successful exploits for bugs in the coming month. Microsoft tagged all three of today’s bugs with a “3” on its 1-3 exploitability index. According to the company, a “3” means “functioning exploit code is unlikely.”

“I’m guessing that they determined that the default configuration [of the software] and the default configuration of the [Windows] firewall are going to mitigate a huge amount of any potential exploitation,” said Storms.

This is not the first time in recent memory that Microsoft has patched the SMB protocol. In November, it fixed an SMB flaw that had been first disclosed more than seven years earlier. And in October, it patched a less dangerous buffer overflow bug in SMB.

“That’s three in four months,” said Storms, “and it points to a pattern.” He speculated that researchers who reported this month’s vulnerabilities used information disclosed in the last two SMB updates to find these newest flaws.

Some researchers paid nearly as much attention to what Microsoft did not patch today as they did to what it fixed.

“I definitely expected a patch for SQL Server by now,” said Wolfgang Kandek, Qualys’ chief technology officer. “I’m not sure what’s happening here, but until last week, we were all geared up for that fix.”

Last month, Microsoft acknowledged a critical vulnerability in older versions of its widely-used SQL Server database software, and it said attack code had been released. It has not fixed the flaw, however.

A day after acknowledging that SQL Server vulnerability, Microsoft confirmed that it started work on that flaw in April 2008, but it declined to say whether it has had a patch ready since September, as an Austrian security researcher alleged.

“I think there’s certainly the potential for Microsoft to go ‘out-of-band’ on this,” said Shavlik’s Schultze, referring to the rare practice where Microsoft issues a security update outside of its once-a-month schedule. “Microsoft’s getting enough heat about it for that to happen.”

But his more immediate concern remained the SMB bugs Microsoft patched today. “If a worm is released, and that worm makes it into a corporate network, it will make Swiss cheese of that network relatively quickly,” Schultze said.

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