Tag Archives: SafeSEH

Half a Dozen Windows Updates; One Critical

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

Severity: High


  • These vulnerabilities affect: All current versions of Windows and components that ship with it
  • How an attacker exploits them: Multiple vectors of attack, including  enticing your users to download and open malicious media, documents, or other files.
  • Impact: Various results; in the worst case, an attacker can gain complete control of your Windows computer
  • What to do: Install the appropriate Microsoft patches immediately, or let Windows Automatic Update do it for you.


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.

  • MS12-004: Two Windows Media Code Execution Flaws

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

  • MS12-001: Windows Kernel SafeSEH Bypass Vulnerability

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

  • MS12-002: Code Execution Vulnerability in Windows Object Packager

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

  • MS12-003CSRSS Elevation of Privilege Vulnerability

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.

  • MS12-005: Microsoft ClickOnce Code Execution Flaw

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.

  • MS12-006: SSL/TLS Protocol Vulnerability (BEAST Attack)

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.


Microsoft has released patches correcting these issues.


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



Seven Microsoft Security Bulletins in January; Two Fix Issues in Security Mechanisms

Like clockwork, Microsoft has posted the first Patch Day of the new year. In a word, I’d summarize it as average.

As they forewarned in their advanced notification last week, Microsoft released seven security bulletins today, which include six updates for Windows and one update for a Microsoft development tool (specifically an AntiXSS library). They only rate one of the Windows bulletins as Critical, but some of the Important bulletins also fix significant flaws that could allow attackers to execute code (though with more user interaction or difficulty).

One noteworthy aspect of today’s Patch Day is that two of the bulletins fix flaws within some Microsoft security mechanisms. One update fixes a flaw in SafeSEH, a Windows security mechanism that makes it more difficult for attackers to leverage buffer overflow or memory corruption flaws. Another bulletin fixes an information disclosure flaw in AntiXSS, a developer library that Microsoft offers to ASP.NET coders. AntiXSS is essentially an encoding library that helps web developers sanitize user input in their web applications. Sanitizing such input helps prevent your web application from suffering from cross-site scripting (XSS) vulnerabilities.

Though I find the security mechanism issues more interesting, the most severe bulletin in today’s batch corrects two serious issues in Windows’ media handling components. By enticing you to play maliciously crafted media, and attacker could exploit these issues to execute code on your computer, potentially gaining full control of it.

You can learn more about today’s updates in Microsoft’s January summary bulletin, which lists the bulletins from the most to least severe. Microsoft’s severity ratings seem right on to me, this month, so I recommend you apply the updates in that order. As is normally the case with Microsoft updates, you should probably test the patches before deploying them in your production network — especially ones that affect your production servers.

I’ll post a more detail, consolidated Windows alert here, shortly. However, I’ll probably not post a detailed alert about the AntiXSS update,  since I suspect few of our readers and customers use it. That said, if you are a security minded ASP.NET developer that does leverage this library, you should definitely refer to Microsoft’s bulletin for its patch.

NOTE: Today is technically Adobe Patch Day as well, and they have released a security bulletin concerning Reader and Acrobat. We’ll post a more detailed alert about this Reader update too, but concerned Adobe users can download and install it now. Just refer to the Solution section of this bulletin– Corey Nachreiner, CISSP


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