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Half a Dozen Windows Updates; One Critical

Corey Nachreiner

Bulletins Affect Windows Media components, CSRSS, SSL/TLS, and More

Severity: High

Summary:

Exposure:

Today, Microsoft released six security bulletins describing seven vulnerabilities affecting Windows and components that ship with it. Each vulnerability affects different versions of Windows to varying degrees. However, a remote attacker could exploit the worst of these flaws to gain complete control of your Windows PC. The summary below lists the vulnerabilities, in order from highest to lowest severity.

Windows ships with media rendering components, such as Windows Media Player and DirectShow, to allow users to play various types of multimedia. Unfortunately, these two Windows Media components suffer from code execution vulnerabilities. Though the flaws differ technically, and affect separate components, they share a similar scope and impact. By enticing you to open a specially crafted media file, an attacker can exploit these flaws to execute code on your user’s computer, with that user’s privileges. Since typical Windows users tend to have local administrative privileges, attackers can often exploit these types of flaws to gain complete control of your machine.

Microsoft rating: Critical

Over the years. Microsoft has introduced various Data Execution Prevention (DEP) mechanisms into Windows, which are designed to make it more difficult for attackers to leverage memory corruptions vulnerabilities, such as buffer overflow attacks. Without going into too much technical depth, these DEP mechanisms generally make it more difficult for attackers to inject and execute shellcode from memory locations typically reserved for non-executable data. SafeSEH is just another DEP-related mechanisms that tries to prevent attackers from hijacking Windows’ Structured Exception Handler (SEH) during a buffer overflow attack. Unfortunately, an external researcher discovered a way to bypass Windows’ SafeSEH security mechanism. In itself, this security bypass flaw is not a direct vulnerability in Windows. In other words, an attacker can’t directly leverage it to gain control of your computer. However, if an attacker were to discover a new buffer overflow vulnerability in Windows, this SafeSEH flaw would make it easier for the attacker to bypass Windows’ DEP protections, and exploit the buffer overflow attack.

Microsoft rating: Important

According to Microsoft, the Windows Object Packager is “a tool that can be used to create a package that can be inserted into a file.” As that definition is quite vague, we prefer the one found in PC Magazine’s glossary, which relates the Object Packager to Object Linking and Embedding (OLE); a Microsoft technology which allows you to embed one Microsoft document within another. In any case, the Windows Object Packager suffers from an unspecified implementation flaw, which attackers can leverage to trick users into accidentally running potentially malicious executable files. By enticing you to open a seemingly legitimate file containing a specially packaged object from the same share or network location as a malicious executable file, an attacker can force you to run that executable file even though you didn’t specifically interact with it. This Object Packager flaw only affects Windows XP and Server 2003.

Microsoft rating: Important

The Client/Server Run-time SubSystem (CSRSS) is an essential Windows component responsible for console windows and creating and deleting threads. It suffers from a local privilege elevation issue. By running a specially crafted application, an attacker can leverage this flaw to execute code with full system privileges, regardless of his actual user privilege. However, in order to run his special program, the attacker would first need to gain local access to your Windows computers using valid credentials. This factor significantly reduces the risk of this flaw.

Microsoft rating: Important.

Microsoft ClickOnce is a deployment technology that makes it easy for developers to create self-updating windows applications that are easy to install. Unfortunately, it turns out ClickOnce applications are much to easy to install. Microsoft has not included ClickOnce files in the Windows Packager’s unsafe file type list. As a result, if you open a specially crafted Office documents containing a ClickOnce application, the application runs automatically. Attackers can leverage this flaw to trick your users into accidentally installing malware by simply opening innocuous looking documents.

Microsoft rating: Important.

Last September, researchers at the Ekoparty Security Conference demonstrated the BEAST SSL/TLS attack. BEAST stands for Browser Exploit Against SSL/TLS and takes advantage of vulnerabilities in the  SSL/TLS protocol to intercept and decrypt HTTPS requests. This The Register article contains a fairly good high-level summary of the BEAST tool and this attack. Microsoft’s MS12-006 update mitigates this SSL/TLS protocol vulnerability.

Microsoft rating: Important.

Solution Path:

Microsoft has released patches for Windows which correct all of these vulnerabilities. You should download, test, and deploy the appropriate Windows patches throughout your network immediately. If you choose, you can also let Windows Update automatically download and install these updates for you.

In the past, we’ve shared individual links for all the updates from Microsoft’s security bulletins in our own alert. However, Microsoft does an excellent job of providing and organizing these update links in their own bulletins. In the future, rather than providing these update links individually, we will refer you to the “Affected and Non-Affected Software” section of the individual Microsoft’s bulletins. Feel free to let us know if you don’t like this change in the comments section of this post.

The links below should take you directly to the “Affected and Non-Affected Software” section of each bulletin, where you can find links for the various updates:

For All WatchGuard Users:

Attackers can exploit these flaws using diverse exploitation methods. A properly configured firewall can mitigate the risk of some of these issues. Furthermore, WatchGuard’s proxy policies can block some of the content necessary to exploit some of these flaws. That said, our appliances cannot protect you from local attacks, nor can it prevent attacks that leverage normal HTTP traffic. Therefore, installing Microsoft’s updates is your most secure course of action.

Status:

Microsoft has released patches correcting these issues.

References:

This alert was researched and written by Corey Nachreiner, CISSP.

 

 

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