On Saturday, April 26 Microsoft announced that Internet Explorer version 6 until version 11 is under potential risk against drive-by attacks from malicious websites, regardless of the underlying Microsoft operating system and the associated memory protection features integrated with the operating system. Microsoft has assigned CVE-2014-1776 to this unknown use-after-free vulnerability, which in the worst case could allow remote code execution if a user views a specially crafted website. If an attacker successfully exploits this vulnerability, s/he will gain the same rights and privileges as the current user (once again, activated User Account Control [UAC] helps keeping privileges of the user low).
The recommended mitigating controls from Microsoft, especially unregistering the VGX.DLL library has led to the misunderstanding, that many people thought the vulnerability is located in the VGX.DLL library. That is wrong. Instead, the vulnerability is located in mshtml.dll, mshtml.tlb, Microsoft-windows-ie-htmlrendering.ptxml, and Wow64_microsoft-windows-ie-htmlrendering.ptxml and therefore unregistering of the above library does not globally mitigate the vulnerability. It only mitigates a specific attack vector where Vector Markup Language (VML) is being used during the attack. Continue reading “The Role of VGX.DLL in the Context of the Latest IE 0-Day”
Actually a Windows Vulnerability (Microsoft Advisory 2757760) related to the Internet Explorer Version 7, 8 and 9 is in the news. Microsoft is aware of the problem, but there’s no patch available yet. We call this a 0-Day :-). Making the problem even worse, on monday reliable exploit code was released within the Metasploit project, so exploit code is already in the wild.
Disabling Active X and Active Scripting in the Internet Settings
But both of them have some impact: EMET must be deployed before any usage (btw. EMET can be configured via Group Policies) and disabling Active X and Active Scripting might break some business relevant web sites (that can be added to the “Trusted Sites” Zone, but might produce major operational effort).
There are more possible mitigating controls, so let’s just summarize some ideas:
Use of alternative browser: if you have it deployed already, go for it :-). Otherwise we have the same deployment issue as with EMET.
Sandboxing/Application Virtualization: It’s the same as with the alternate browser, of you have it, go for it, otherwise it will be a long term project. And be aware that also Application Virtualization won’t address all issues (see the ERNW Newsletter 32 for details).
No local admin rights: This doesn’t protect from exploiting the vulnerability, but at least reduces the impact. We strictly recommend to check the local administrator group and remove all users that don’t rely on it for fulfilling their business tasks. And btw. this topic is not new ;-), see also ERNW Newsletter 4, published in 2004!
Blocking communication for the clients at the corporate firewall: Be aware that this doesn’t really work. Modern exploit code is able to use the corporate proxy infrastructure including authentication to circumvent this control. Metasploit has exploit payloads for this.
Disabling/Blocking Flash content: While potentially not strictly required for exploitation, at least in some of the exploits currently observed in the wild Adobe Flash plays a major role. So like discussed in these Insinuator posts (1, 2 and 3), restricting the use of Adobe Flash would proactively prevent some known exploits from working. But the newly published Metasploit exploit doesn’t use Flash, so keep in mind that this mitigating control can only be used in addition to other ones.
So for a short term mitigation we recommend the following (especially for corporate environments)
Disabling Active X and Active Scripting via Group Policies
Disable/block Flash content
Remove unneeded local administrative privileges
If available use alternative browser or EMET
For long term mitigation (might also be feasible in small environments as short term mitigation):
Evaluate possibilities of application sandboxing/virtualization
Deploy alternative browser. Be aware that deploying a second browser might not be an option for big corporate environments (central management and supporting/maintaining additional software are the main reasons for this).
And finally DON’T PANIC ;-), start to address the problem in a professional way.