Security Corner

Dec 12 2008   9:44PM GMT

Internet Explorer Targeted by Zero-day Attack

Ken Harthun Ken Harthun Profile: Ken Harthun

Even though Microsoft released the biggest batch of patches ever on Tuesday–28 flaws affecting Windows, Office, Internet Explorer, Visual Basic Active Controls and Windows Media Player, 23 of them rated “critical”–there’s no fix for a zero-day XML parser vulnerability that surfaced the same day. This was first reported by Robert McMillan of IDG News and was picked up quickly by other media. According to McMillan:

The code exploits a bug in the way IE handles XML (Extensible Markup Language) and works on the browser about “one in three times,” Huang said in an instant message interview. For the attack to work, a victim must first visit a Web site that serves the malicious JavaScript code that takes advantage of the flaw. …

In attacks, the code drops a malicious program on the victim’s PC which then goes to download malicious software from various locations.

According to a blog post by Symantec:

The vulnerability is caused by a function that incorrectly frees a certain region of heap memory so that an attacker is able to control the EAX register with a specially crafted Unicode URL, which includes the magic “0x0A0A” value in it,” Elia Florio, a security researcher at Symantec, wrote….

Symantec released the antivirus signature Bloodhound.Exploit.219 and IPS signature 23241 – HTTP MSIE Malformed XML BO to protect users against this exploit.

I recommend that anyone using Symantec’s antivirus or IPS products, immediately perform an update. Furthermore, Symantec recommends blocking the following hosts which are apparently being used by the exploit to download and install other malware:


In its security advisory 961051, Microsoft presents the following mitigating factors:

• Protected Mode in Internet Explorer 7 and Internet Explorer 8 in Windows Vista limits the impact of the vulnerability.

•By default, Internet Explorer on Windows Server 2003 and Windows Server 2008 runs in a restricted mode that is known as Enhanced Security Configuration. This mode sets the security level for the Internet zone to High. This is a mitigating factor for Web sites that you have not added to the Internet Explorer Trusted sites zone.

•An attacker who successfully exploited this vulnerability could gain the same user rights as the local user. Users whose accounts are configured to have fewer user rights on the system could be less affected than users who operate with administrative user rights.

•Currently known attacks cannot exploit this issue automatically through e-mail.

Nevertheless, users should avoid using Internet Explorer and should instead use Firefox with the NoScript extension installed until Microsoft issues a patch. We may see an out-of-cycle patch on this one according to the security advisory:

We are actively investigating the vulnerability these attacks attempt to exploit. We will continue to monitor the threat environment and update this advisory if this situation changes. On completion of this investigation, Microsoft will take the appropriate action to protect our customers, which may include providing a solution through a service pack, our monthly security update release process, or an out-of-cycle security update, depending on customer needs.

Well, since I’m forced to use IE for certain applications in my job, this customer needs a patch as quickly as possible.

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