Microsoft on Saturday confirmed that Internet Explorer (IE) 6, 7 and 8 contain an unpatched bug -- or "zero-day" vulnerability -- that is being used by attackers to hijack victims' Windows computers.
The company is "working around the clock" on a patch, its engineers said. They have also released a preliminary workaround that will protect affected IE customers until the update is ready.
In a security advisory issued Dec. 29, Microsoft acknowledged that attacks are taking place. "Microsoft is aware of targeted attacks that attempt to exploit this vulnerability through Internet Explorer 8," the alert stated.
Newer versions of IE, including 2011's IE9 and this year's IE10, are not affected, Microsoft said. It urged those able to upgrade to do so.
According to multiple security firms, the vulnerability was used by hackers to exploit Windows PCs whose owners visited the website of the Council on Foreign Relations (CFR), a non-partisan foreign policy think tank with offices in New York and Washington, D.C.
On Friday, FireEye corroborated earlier reports that the CFR website had been compromised by attackers and was hosting exploit code as early as Dec. 21. As of mid-day Wednesday, Dec. 26, the site was still conducting "drive-by" attacks against people running IE8, said Darien Kindlund, senior staff scientist at FireEye, in a Friday blog.
Kindlund added that the malware hidden on the CFR website used Adobe Flash Player "to generate a heap spray attack" against IE8. It wasn't clear whether Flash also contained a zero-day bug, or whether the attackers leveraged an already-known and previously patched vulnerability that had not been fixed on the victims' PCs.
On Saturday, Jaime Blasco, the labs manager at AlienVault, weighed in on the IE zero-day as well, noting that the exploit was able to circumvent Microsoft's anti-exploit technologies, DEP (data execution prevention) and ASLR (address space layout randomization), and successfully compromise Windows XP and Windows 7 PCs running IE8. He identified the IE bug as a likely "use-after-free" vulnerability, a type of memory management flaw.
AlienVault, said Blasco, had begun looking into the "watering hole" attacks stemming from the CFR website at the beginning of the week, and had alerted the Microsoft Security Response Center (MSRC) that it suspected IE harbored a zero-day vulnerability.
In a watering hole campaign, hackers identify their intended targets, even to the individual level, then scout out which websites they frequently visit. Attackers next compromise one or more of those sites, plant malware on them, and like a lion waits at a watering hole for unwary wildebeests, wait for unsuspecting users to surf there.
The CFR did not immediately reply to a request for comment on its site's current status.
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