Summary:
This vulnerability affects: All current versions of Internet Explorer
How an attacker exploits it: Mostly by enticing one of your users to visit a web page containing malicious content
Impact: Various, in the worst case an attacker can execute code on your user's computer, potentially gaining complete control of it
What to do: Deploy the appropriate Internet Explorer patches immediately, or let Windows Automatic Update do it for you
Exposure:
In a security bulletin released today as part of Patch Day, Microsoft describes an update that fixes a whooping 59 new vulnerabilities that affect all current versions of Internet Explorer (IE). Microsoft rates the aggregate severity of these new flaws as Critical.
The biggest story about today's IE update is the sheer number of vulnerabilities it corrects. I don't think I remember a Microsoft update that fixed more flaws than this one. While all 59 of these flaws are technically different, most of them share the same general scope and impact, and involve memory corruption flaws having to do with how IE handles certain HTML objects. If an attacker can lure one of your users to a web page containing malicious web code, he could exploit many of these memory corruption vulnerabilities to execute code on that user's computer, inheriting that user's privileges. Typically, Windows users have local administrative privileges. In that case, the attacker could exploit these flaws to gain complete control of the victim's computer.
The update also includes fixes some information disclosure and elevation of privileges flaws as well, but the memory corruption issues pose the most risk. Technical differences aside, this is a very important IE update that plugs many serious holes in IE. Furthermore, this update also fixes a zero day IE flaw that the Zero Day Initiative (ZDI) disclosed a few weeks ago. You should download and install the IE cumulative patch immediately.
Keep in mind, today’s attackers often hijack legitimate web pages and booby-trap them with malicious code. Typically, they do this via hosted web ads or through SQL injection and cross-site scripting (XSS) attacks. Even recognizable and authentic websites could pose a risk to your users if hijacked in this way, and the vulnerabilities described in today’s bulletin are perfect for use in drive-by download attacks.
Solution Path:
You should download, test, and deploy the appropriate IE updates immediately, or let Windows Automatic Update do it for you. You can find links to the various IE updates in the “Affected and Non-Affected Software” section of Microsoft’s April IE security bulletin.
