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One week after confirming a code execution flaw in its flagship Internet Explorer browser, Microsoft has shipped a “killbit” package to disable the affected control, javaprxy.dll.
The killbit, also known as a registry key update, is one of seven pre-patch workarounds in a revised security bulletin released by software engineers at the Microsoft Security Response Center.
Since the advisory was first issued on June 30, Microsoft Corp. has pushed out two revisions with new information to counter the public release of exploit code on security Web sites and mailing lists.
In addition to the killbit package, which will be part of a future security bulletin, Microsoft is also recommending that users set Internet and local intranet security zone settings to “High” before running ActiveX controls in these zones.
Other temporary workarounds include unregistering the Javaprxy.dll COM Object; setting Internet Explorer to prompt before running or disable ActiveX controls in the Internet and Local intranet security zone; modifying the Access Control List on Javaprxy.dll to be more restrictive; or using a Software Restriction Policy to restrict access to Javaprxy.dll in IE on Windows XP and later versions.
Microsoft has also suggested that IE users might choose to permanently remove the MSJVM (Microsoft Java Virtual Machine) from their systems. The company said the MSJVM Diagnostic Tool can be used to perform remote and local scans to detect for the presence of MSJVM and MSJVM-related software.
“Customers can then use the Java Removal Tool to permanently remove the Microsoft Java Virtual Machine from their system,” according to the advisory. However, Microsoft cautioned that the removal of MSVVM from a system is permanent.
“Microsoft cannot provide Windows operating system recovery media to you that includes the MSJVM for reinstallation. Microsoft no longer includes the MSJVM in Windows operating system products,” the company said. “Applications that require the Microsoft Java Virtual Machine will no longer function correctly.”
The software giant has already warned that the security flaw could be exploited by malicious hackers to take “take complete control of the affected system,” and the existence of zero day exploits before Microsoft could ship a cumulative IE patch has raised fears that a widespread attack could be imminent.
All supported versions of Internet Explorer, including IE 6.0 in Windows XP Service Pack 2, are affected.
The bug, which was discovered and reported by security research firm SEC Consult, could be exploited to crash the browser or execute arbitrary code in the context of IE. Microsoft said it was not aware of any customer impact, such as attacks attempting to use the reported vulnerability, and promised that a patch would be made available once an investigation is completed.
“A COM object, javaprxy.dll, when instantiated in Internet Explorer can cause Internet Explorer to unexpectedly exit. We are investigating a potentially exploitable condition,” Microsoft said.
The company said that a successful attacker could exploit the flaw by creating a malicious Web page and persuading the user to visit the page. An attacker could also attempt to compromise a Web site to have it display a Web page with malicious content to try to exploit this vulnerability.
More details on pre-patch workarounds and other information can be found in the Microsoft security advisory.