“Use After Free” Flaws: A New Theme for IE Vulnerability

“Use After Free” Flaws: A New Theme for IE Vulnerability

Severity: High


  • These vulnerabilities affect: Most current versions of Internet Explorer (IE)
  • How an attacker exploits them: By enticing one of your users to visit a malicious web page
  • Impact: An attacker can execute code on your user’s computer, often gaining complete control of it
  • What to do: Install Microsoft’s IE updates immediately, or let Windows Automatic Update do it for you


As part of today’s Patch Day, Microsoft released a security bulletin describing two new security vulnerabilities affecting Internet Explorer (IE). Similar to the flaws in last month’s update, both of these vulnerabilities are what developers call “use after free” vulnerabilities – a type of memory corruption flaw that attackers can leverage to execute arbitrary code. This class of vulnerability seems to be a theme for IE lately, since Microsoft has been fixing IE use after free flaws quite a bit over the last few months.

In any case, if an attacker can lure one of your users to a web page containing maliciously crafted HTML, she could exploit either of these vulnerabilities to execute code on that user’s computer, inheriting that user’s privileges. Typically, Windows users have local administrative privileges, in which case the attacker can exploit these flaws to gain complete control of the victim’s computer.

If you’d like more technical detail about either of these flaws, see the “Vulnerability Information” section of Microsoft’s bulletin. Technicalities aside, both of these remote code execution flaws pose significant risk to IE users, and allow attackers to launch drive-by download attacks. Attackers often hijack legitimate web sites and force them to serve this kind of malicious web code. So these types of flaws may affect you even when visiting legitimate, trusted web sites.

If you use IE, you should download and install Microsoft’s cumulative update immediately.

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 IE security bulletin.

For All WatchGuard Users:

WatchGuard’s Gateway Antivirus services can often prevent the malware that drive-by download attacks try to force onto your computer. Furthermore, our Reputation Enabled Defense (RED) and WebBlocker service can often prevent your users from accidentally visiting malicious sites. Nonetheless, we still recommend you install Microsoft’s IE update to completely protect yourself from these vulnerabilities.


Microsoft has released patches to fix these vulnerabilities.


This alert was researched and written by Corey Nachreiner, CISSP (@SecAdept).

Published with permission from WatchguardWire. Source.

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