- These vulnerabilities affect: All current versions of Windows or components often packaged with it (like the .NET Framework)
- How an attacker exploits them: Multiple vectors of attack, including sending specially crafted network traffic or running malicious programs locally
- Impact: Varies, ranging from a remote Denial of Service (DoS) attack to local attackers gaining complete control of your Windows computer
- What to do: Install the appropriate Microsoft patches as soon as possible, or let Windows Automatic Update do it for you
Today, Microsoft released three security bulletins that describe six vulnerabilities affecting Windows or components related to it (like the .NET Framework). They only rate these bulletins as Important, due to limited impact or mitigating factors. Each of these vulnerabilities affects different versions of Windows to varying degrees. In the worst case, a local attacker could exploit one of these flaws to gain complete control of your Windows PC. We recommend you download, test, and deploy these updates at your earliest convenience.
The summary below lists the vulnerabilities, in order from highest to lowest severity.
- MS13-039: HTTP.sys DoS Vulnerability
The HTTP Protocol Stack (HTTP.sys) is a Windows component that listens for and handles HTTP requests before passing them to a web server like IIS. It suffers from a Denial of Service (DoS) vulnerability having to do with its inability to properly handle HTTP requests with specially malformed headers. By sending a specially crafted HTTP request, a remote attacker can leverage this flaw to cause your system to stop responding. While this sort of DoS attack doesn’t result in any breach or data loss, attackers can leverage it to knock your public web server offline, which could have significant business implications. You should download, test, and deploy Microsoft’s HTTP.sys update as soon as possible.
Microsoft rating: Important
- MS13-040: Multiple .NET Framework Vulnerabilities
The .NET Framework is a software framework used by developers to create custom Windows and web applications. Though it only ships by default with Windows Vista, you’ll find it on many Windows computers. The .NET Framework component suffers from two new security vulnerabilities.
The first issue is an XML digital signature spoofing vulnerability. XML files can contain digital signatures, which .NET applications can use to verify the integrity of XML files (ensuring they haven’t been improperly modified). However, the .NET Framework component (CLR) responsible for validating these signatures doesn’t do it right. As a result, attackers can modify the contents of an XML file without invalidating the signature. The impact of this flaw depends on if and how your custom .NET applications leverage this functionality.
The second issue is an authentication bypass vulnerability. The Windows Communication Foundation (WCF) is essentially a set of .NET APIs that developers can use to make applications that communicate securely with one another. However, WCF suffers from an authentication bypass flaw. By sending specially crafted packets, an attacker could gain unauthenticated access to computers that run WCF services. The impact of this bypass depends on your custom .NET application. If you custom application gives your users access to sensitive data, then in can pose a significant risk. If you install the .NET framework, you should download, test, and install Microsoft’s update as soon as you can.
Microsoft rating: Important
- MS13-046: Kernel-Mode Driver Elevation of Privilege Flaws
The kernel is the core component of any computer operating system. Windows also ships with a kernel-mode device driver (win32k.sys), which handles the OS’s device interactions at a kernel level. The Windows kernel-mode driver suffers from three new local elevation of privilege flaws. They all differ technically, but share the same basic scope and impact. By running a specially crafted program, a local attacker could leverage this flaw to gain complete control of your Windows computers (or cause it to become unstable). However, in order to run his malicious program, the attacker would first need to gain local access to your computer or trick you into running the program yourself, which significantly lessens the severity of this vulnerability.
Microsoft rating: Important
Microsoft has released Windows and .NET Framework patches that correct all of these vulnerabilities. You should download, test, and deploy the appropriate updates throughout your network immediately. If you choose, you can also let Windows Update automatically download and install them for you.
The links below point directly to the “Affected and Non-Affected Software” section of each bulletin, where you can find links to the various updates:
For All WatchGuard Users:
WatchGuard’s Gateway Antivirus and Intrusion Prevention services can often prevent some of these types of attacks, or the malware they try to distribute. For instance, our IPS signature team has developed signatures that can detect and block a few of the issues described above, including:
- WEB Microsoft Windows 2012 Server HTTP.sys Denial of Service Vulnerability (CVE-2013-1305)
- EXPLOIT Microsoft XML Digital Signature Spoofing Vulnerability (CVE-2013-1336)
Your XTM appliance should get this new IPS update shortly.
However, attackers can exploit some of these flaws in other ways, including by convincing users to run executable files locally. Since your gateway appliance can’t protect you against local attacks, we still recommend you install Microsoft’s updates to completely protect yourself from these flaws.
Microsoft has released patches correcting these issues.
- Microsoft Security Bulletin MS13-039
- Microsoft Security Bulletin MS13-040
- Microsoft Security Bulletin MS13-046
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