Unpatched Critical IE Browser Zero-Day Vulnerability Affected Millions of Windows Users

Microsoft issued a warning about critical IE Zero Day vulnerability that actively exploited in wide and warns millions of Windows users

A critical remote code execution vulnerability exists in the way that the scripting engine handles objects in memory in Internet Explorer.

Internet Explorer is one of the widely used web browsers developed by Microsoft and included in the Microsoft Windows line of operating systems, starting in 1995.

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Based on the Browser Market Share report, Internet Explorer is a 3rd web browser next to Chrome and Firefox with a 7.44% market share and is used by millions of users around the world including within corporate networks. 

Successful exploitation of this IE Zero day vulnerability lets an attacker corrupt memory in such a way that it could execute arbitrary code in the context of the current user. 

An attacker could successfully exploit this vulnerability to gain the current user access, and if the user logged in as admin, an attacker could gain complete control of the vulnerable system.

In results, an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

According to Microsoft advisory, “In a web-based attack scenario, an attacker could host a specially crafted website that is designed to exploit the vulnerability through Internet Explorer and then convince a user to view the website, for example, by sending an email.”

Affected Version:

Mitigation:

Currently, there is no patch available for this IE Zero Day vulnerability, Microsoft issued advisory mitigation.

Restrict access to JScript.dll

For 32-bit systems, enter the following command at an administrative command prompt:

    takeown /f %windir%\system32\jscript.dll
    cacls %windir%\system32\jscript.dll /E /P everyone:N

For 64-bit systems, enter the following command at an administrative command prompt:

    takeown /f %windir%\syswow64\jscript.dll
    cacls %windir%\syswow64\jscript.dll /E /P everyone:N
    takeown /f %windir%\system32\jscript.dll
    cacls %windir%\system32\jscript.dll /E /P everyone:N

By default, IE11, IE10, and IE9 uses Jscript9.dll which is not impacted by this vulnerability. This vulnerability only affects certain websites that utilize jscript as the scripting engine.

Microsoft working to fix the vulnerability and the security update can be expected soon the same as the other IE zero day vulnerability that fixed last year.