Microsoft has issued an advisory to help users deal with a zero-day flaw affecting Internet Explorer.
In an update, Microsoft stated the flaw affects not only Internet Explorer (IE) 7 as originally thought, but also versions 5 and 6. However, as of Dec. 11, Microsoft had only seen attacks against IE 7.
While the flaw was initially thought to lie primarily in the X M L parsing engine, Microsoft confirmed it actually goes beyond that.
"The vulnerability exists as an invalid pointer reference in the data binding function of Internet Explorer," according to Microsoft. "When data binding is enabled (which is the default state), it is possible under certain conditions for an object to be released without updating the array length, leaving the potential to access the deleted object's memory space. This can cause Internet Explorer to exit unexpectedly, in a state that is exploitable."
News of the flaw, which affects IE on multiple platforms, began to circulate Dec. 10 as hackers launched attacks. The vulnerability remains under investigation by Microsoft.
While users await a patch or an update, Microsoft has offered up a few workarounds customers can use to help thwart attacks. First, the company recommends users change the Internet and local intranet security settings to "High" so there will be prompts before running of ActiveX controls and active scripting in these zones.
Other advice includes configuring IE to prompt before running active scripting or to disable it in the Internet and local intranet security zone. Enabling DEP (Data Execution Prevention) is also recommended as a workaround.
"Setting the Internet zone security setting to High protects against all currently known exploits of this vulnerability by disabling scripting [and] disabling less secure features in Internet Explorer, and blocks known techniques used to bypass Data Execution Prevention," the Microsoft advisory stated.
According to Microsoft, the attacks are being launched against IE 7 on supported editions of Windows XP Service Pack 2, Windows XP SP3, Windows Server 2003 Service Pack 1, Windows Server 2003 SP2, Windows Vista, Windows Vista SP1 and Windows Server 2008.
*This story was updated to reflect new information that the flaw also affects IE versions 5 and 6, as well as new information about the vulnerability.