Highlighting the risks of releasing security updates on a monthly patching cycle, the software makers MS06-055 bulletin comes a full eight days after virus hunters first spotted the zero-day attacks circulating on porn sites hosted in Russia.
"This reminds me so much of the WMF attacks earlier this year," said Roger Thompson, chief technology officer at Exploit Prevention Labs, in Atlanta. "It came out of left field, ran undetected for a week or three, and by the time the official, emergency patch came out, the damage was done."
"In eight days, the bad guys replenished their botnets, made their money and moved on to the next zero-day. Now the industry is struggling to clean up and chase the copycats," Thompson said.
Microsoft has maintained throughout the episode that the attacks were limited in nature, but, according to data from VeriSigns iDefense, approximately 2,000 domains were hijacked and seeded with code to redirect users to hostile VML websites.
HostGator, an ISP based in Houston, said VML attackers compromised its servers via an unrelated zero-day flaw in the cPanel control panel software distributed with hosting accounts and redirected legitimate Web sites to malicious pages hosting VML exploits.
The exploits then dumped massive amounts of spyware, Trojans, bots and rootkits onto vulnerable Windows machines.
Ken Dunham, director of iDefenses rapid response team, said the exploit sites were using the WebAttacker tool kit to plant malicious code on machines with Windows XP SP2 and older versions of the operating system.
Thompson said its naïve to think that the attackers only hit the malicious sites discovered by virus research firms. "They used two zero-day flaws on disparate operating systems, and that takes some careful planning," he said.
Microsofts MS06-055 bulletin provides fixes for IE 5.01 and IE 6.0 on Windows XP (Service Pack 1 and SP2) and Microsoft Windows Server 2003 (including SP1).
There are no patches for Windows 2000 SP3 and other down-level operating system versions that are vulnerable to the flaw.
According to timestamps in the Microsoft bulletin, the company started updating the vulnerable Vgx.dll library on Sep. 18, 2006, the same day researchers at Sunbelt Software detected the exploits in the wild.
The release of Microsofts update follows the emergence of a high-profile volunteer group called ZERT (Zeroday Emergency Response Team) that created a third-party fix as a stop-gap measure to help mitigate the threat.
The ZERT group has withdrawn its patch and is pointing users to Microsofts official fix.
Editors Note: This story was updated regarding the status of the ZERT patch.