For the first time in a little over four months, Microsoft published an emergency advisory and Fix it for users of its Internet Explorer web browser.
Exploitation of Internet Explorer 8 and 9 has already been witnessed in the wild. That doesn’t necessarily mean that users of Internet Explorer 6, 7, 10 and 11 are safe however.
The only unaffected Windows platforms are the server platforms that ship with IE in restricted mode by default. If you have disabled the restricted mode, these may also be vulnerable.
The flaw is being referenced as CVE-2013-3893 and when exploited successfully results in remote code execution (RCE) as the logged in user.
This is one of the reasons we frequently advise users not to run as an administrator for everyday tasks like internet browsing.
If an attacker wants to inflict more serious damage he will need to also use a elevation of privilege (EoP) exploit to gain more access to the victim PC.
There are several different ways to protect yourself until an official fix from Microsoft becomes available.
For more advanced users and corporate IT managers you can use Microsoft EMET to mitigate exploitation of this flaw as recommended in Microsoft’s advisory 2887505.
For everyday Windows users Microsoft is also providing a “Fix it” download that changes your settings to provide protection until a permanent fix is available, but this only works in 32 bit versions of Internet Explorer.
My advice for non-corporate PCs is to simply use another browser until Microsoft is able to deliver a fix. There are many choices including Firefox, Chrome, Safari and Opera.
We will keep an eye out for any updates on this vulnerability and alert our readers as soon as a permanent fix is available. Typically Microsoft will release an update as soon as possible.
Sophos Techknow – Understanding Vulnerabilities
If you want to learn more about remote code execution, information disclosure, denial of service and elevation of privilege flaws, why not give the latest Sophos Techknow a listen?
In 15 minutes Paul Ducklin and I try to explain what all of this vulnerability jargon means in a useful manner to IT administrators.
(18 September 2013, duration 15’08”, size 9.1MB)
5 comments on “Internet Explorer zero-day exploit prompts Microsoft to publish emergency Fix it”
Unfortunately for Windows users, you have to have IE – it's an essential element of Windows. So just using a different browser may not be enough! IE is still there and still potentially vulnerable.
So my suggestion is to use the Fix-it (to try to close the 'hole') but continue to use an alternative browser anyway.
In Windows Vista+ you can disable I.E.
No, not really. All that does is disable the GUI of IE, the core where the vulnerability lies is still running in the background as it's an inherent part of Windows. In W7 and W8 the Updating uses the core of IE to seek the updates and download them even if you have 'disabled' IE.
So I advise running the Fix-It, to work around the vulnerability that remains even when you 'disable' IE, and using a different and up-to-date browser.
What about for those who have 64-bit?
Read the advisory. x64 is vulnerable too.