Microsoft has warned of a new flaw in all available versions of its Internet Explorer web browser: https://technet.microsoft.com/en-US/library/security/2963983

Vulnerability CVE-2014-1776, to give the problem its formal name, allows miscreants to hijack at-risk Windows computers: http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-1776
It's all due to “the way Internet Explorer accesses an object in memory that has been deleted or has not been properly allocated”, the software giant explained on Saturday.

The flaw means the browser “may corrupt memory in a way that could allow an attacker to execute arbitrary code in the context of the current user within Internet Explorer".

"Microsoft is aware of limited, targeted attacks that attempt to exploit [this] vulnerability in Internet Explorer," the software giant added.

"An attacker could host a specially crafted website that is designed to exploit this vulnerability through Internet Explorer and then convince a user to view the website.”

Internet Explorer 6 through 11 are all at risk, on all current versions of Windows from Vista to 8 and Windows Server 2003 to 2012 R2. The bug is understood to be present in IE on Windows XP, although that operating system is no longer supported.

Redmond's recommended reaction to the problem is to deploy version 4.1 of The Enhanced Mitigation Experience Toolkit (EMET), as that software “helps mitigate the exploitation of this vulnerability by adding additional protection layers that make the vulnerability harder to exploit”: http://www.microsoft.com/en-us/download/details.aspx?id=41138

The US Homeland Security's Computer Emergency Readiness Team has urged "users and administrators enable Microsoft EMET where possible and consider employing an alternative web browser until an official update is available": http://www.us-cert.gov/ncas/current-activity/2014/04/28/Microsoft-Internet-Explorer-Use-After-Free-Vulnerability-Being

Microsoft suggests a few other workarounds, such as switching on IE's Enhanced Protected Mode or setting security levels to “High” to stop ActiveX controls and Active Scripting working.

The upside, if there is any, is that Windows Server's default settings make it hard to create the kind of honeypot website that could exploit this flaw.

Microsoft has not said when a patch will arrive, but has hat-tipped FireEye for helping it to find the flaw. The security biz described the bug as a use-after-free blunder.

(ElReg)