May Day! Microsoft's Patch Day is Not Dead… Yet

Despite Microsoft’s recent Ignite Conference announcement—that they’d no longer follow a monthly patch cycle for Windows 10—Patch Tuesday is in full effect for May. Today, Microsoft released 13 security bulletins, including three Critical ones. If you’re a Microsoft administrator, you should get to these updates quickly.

By the Numbers:

Today, Microsoft released 13 security bulletins, fixing a total of 48 security vulnerabilities in many of their products. The affected products include:

• current versions of Windows (and its components),
• Internet Explorer (IE),
• Office,
• SharePoint Server,
• the .NET Framework,
• and Silverlight.

They rate three bulletins as Critical and the rest as Important. As an aside, Microsoft’s main summary post contains a wealth of useful information, including their vulnerability exploitability index, which helps you prioritize the updates based on how dangerous each vulnerability is in the real world.

Patch Day Highlights:

Today’s Patch Day highlights revolve around the Critical rated issues. Most organizations will want to apply the IE update first. Not only does it fix 22 vulnerabilities, but also ones that attackers can leverage in drive-by download attacks, which are one of the most common attacks today.

You should also prioritize the various document related vulnerabilities, since threat actors are increasingly using malicious documents in their spear phishing emails. I recommend you prioritize the Windows Font Driver, Journal, and Office updates as well.

In short, if you apply the updates quickly, in the order Microsoft lists, you’ll do well.

Quick Bulletin Summary:

We summarize the April security bulletins below in order of severity. We recommend you apply the updates in the same order of priority, assuming you use the affected products.

• MS15-043 – Critical – IE Update Corrects 22 Vulnerabilities – You can normally count on Microsoft releasing a cumulative Internet Explorer (IE) update each month, often fixing many memory corruption vulnerabilities. This month’s IE update fixes a slightly more diverse set of flaws, including some privilege elevation issues, and Address Space Layout Randomization (ASLR) bypass vulnerabilities. However, the memory corruption issues still probably pose the highest risk. If an attacker can get you to visit a site with malicious code, he could exploit these flaws to run code on your machine. If you have local administrator privileges, the attacker gains full control of your PC. The other IE flaws also make it easier for attackers to bypass Windows’ security mechanisms, and even gain more privilege on your system. Combined, these are perfect vulnerabilities for attackers to exploit in drive-by download attacks. I’d make this IE update a top priority.

• MS15-044 – Critical – Windows Font Driver Code Execution Flaw – The Font Driver Windows uses to display OpenType and TrueType fonts suffers from two security flaws; one worse than the other. In essence, if an attacker can get you to view a document or web page that contains a maliciously crafted font, he can exploit the more critical flaw to execute arbitrary code on your computer with your privileges.

• MS15-045 – Critical – Six Journal Code Execution Flaws – Journal is the basic word processing or note taking program that ships with Windows. It suffers from six flaws that share the same scope and impact. If an attacker can get you to view a specially crafted Journal document, she can exploit any of these flaws to execute code on your computer, with your privileges.

• MS15-046 – Important – Two Office Code Execution Flaws – Office suffers from two memory corruption flaws with the same scope and impact. If you open a maliciously crafted Office document, an attacker could exploit either flaw to execute code on your computer.

• MS15-047 – Important – SharePoint Code Execution Flaw – SharePoint Server suffers from a somewhat unspecified code execution vulnerability having to do with its inability to properly sanitize uploaded page content. If an attacker can upload specially crafted content to your Sharepoint Server, they could execute code with the server’s W3WP service account (which has less privilege than the full SYSTEM account).

• MS15-048 – Important – Two .NET Framework Vulnerabilities – The Windows Task Scheduler suffers from an elevation of privilege flaw. If an attacker can log onto your Windows system with valid credentials (even underprivileged ones), she can run a program that exploits this flaw to gain complete control of the computer.

• MS15-049 – Important – Silverlight EoP Flaw – Silverlight suffers from an “out of browser” elevation of privilege vulnerability. While most Silverlight applications are supposed to run with limited permissions, attackers could exploit this vulnerability to escape that “privilege sandbox” and run with your user privileges, or higher. However, an attacker would either have to log into your system with valid credentials and run a malicious Silverlight application, or entice you to run such an application yourself.

• MS15-050 – Important – Local SCM EoP Vulnerability – The Windows Service Control Manager (SCM) suffers from a local privilege escalation vulnerability. By running a specially crafted program, an attacker could leverage this flaw to gain elevated privileges on your Windows systems. However, they’d need valid credential on your systems to do so, which somewhat limits the severity of this flaw.

• MS15-051 – Important – Six Kernel-Mode Driver flaws – Windows’ Kernel-Mode driver suffers from six vulnerabilities. The worst is a local elevation of privilege flaw. If a local attacker can run a malicious application, she can exploit this flaw to gain complete control of your Windows computer, regardless of the malicious user’s original privileges. The five remaining flaws are information disclosure issues, that could help an attacker learn more about your system, and potentially bypass some of Window’s security features (like ASLR).

• MS15-052 – Important – Windows Kernel Security Bypass Flaw – Address Space Layout Randomization (ASLR) is a memory obfuscation technique that some operating systems use to make it harder for attackers to find specific things in memory, which in turn makes it harder for them to exploit memory corruption flaws. Kernel ASLR (KASLR) is essentially the same thing, in regards to kernel memory. The Windows kernel suffers from an information disclosure vulnerability which could help attackers bypass this protection. While it doesn’t allow them to execute code alone, it does make it easier for them to exploit other memory based vulnerabilities.

• MS15-053 – Important – VBScript and JScript ASLR Bypass Flaws – Windows’ JScript and VBScript components suffer from ASLR bypass flaws similar to the ones above. Again, these flaws don’t allow an attacker to execute code by themselves, but they do make it easier for them to exploit other memory corruption vulnerabilities.

• MS15-054 – Important – MMC DoS Vulnerability – The Windows Microsoft Management Console (MMC) suffers from flaw in the way it handles icon information in a .MSC file. If an attacker can lure you into running a maliciously crafted .MSC file, they could cause you system to stop responding.

• MS15-055 – Important – Schannel Information Disclosure Flaw – Secure Channel (Schannel) is Microsoft’s SSL/TLS implementation. Schannel still allows the use of a weaker cryptographic key length (specifically a 512-byte DFE key), which is susceptible to known attacks. This update increases the minimum key length, making it harder to crack.

Solution Path:

If you use any of the software mentioned above, you should apply the corresponding updates as soon as you can. I recommend you apply the Critical updates immediately, try to get to the Important ones as a soon as possible.

You can get the updates three ways:

1. Let Windows Automatic Update do it for you – While patches sometimes introduce new problems, these occasional issues don’t seem to affect clients as often as they do servers. To keep your network secure, I recommend you set Windows clients to update automatically so they get patches as soon as possible.
2. Manually download and install patches – That said, most businesses strongly rely on production servers and server software. For that reason, I recommend you always test new server updates before applying them manually to production servers. Virtualization can help you build a test environment that mimics your production one for testing.  You can find links to download the various updates in the individual bulletins I’ve linked above.
3. Download May’s full Security Update ISO –  Finally, Microsoft eventually posts an ISO image that consolidates all the security updates. This ISO conveniently packages the updates in one place for administrators. You’ll eventually find a link to the monthly security ISOs here, but Microsoft may not post it until a few days after Patch Day

For WatchGuard Customers:

Good News! WatchGuard’s Gateway Antivirus (GAV), Intrusion Prevention (IPS), and APT Blocker services can often prevent these sorts of attacks, or the malware they try to distribute. For instance, our IPS signature team has developed signatures that can detect and block many of the attacks described in Microsoft’s alerts:

• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1658)
• FILE Microsoft Windows Journal Remote Code Execution Vulnerability (CVE-2015-1675)
• FILE Microsoft Windows Journal Remote Code Execution Vulnerability
• FILE Microsoft Office Memory Corruption Vulnerability (CVE-2015-1682)
• WEB-CLIENT Microsoft Internet Explorer ASLR Bypass (CVE-2015-1685)
• WEB-CLIENT Microsoft Internet Explorer VBScript and JScript ASLR Bypass (CVE-2015-1686)
• FILE Microsoft Internet Explorer Elevation of Privilege Vulnerability (CVE-2015-1688)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1689)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1691)
• WEB-CLIENT Microsoft Internet Explorer Clipboard Information Disclosure Vulnerability (CVE-2015-1692)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1705)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1706)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1708)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1718)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1717)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1714)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1712)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1711)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1710)
• WEB-CLIENT Microsoft Internet Explorer Memory Corruption Vulnerability (CVE-2015-1709)

Your Firebox or XTM appliance should get this new IPS signature update shortly.

Furthermore, our Reputation Enabled Defense (RED) and WebBlocker services can often prevent your users from accidentally visiting malicious (or legitimate but booby-trapped) web sites that contain these sorts of attacks. Nevertheless, we still recommend you install Microsoft’s updates to completely protect yourself from all of these flaws.

As an aside, Microsoft also released two new security advisories today. If you are interested in how Microsoft is improving their cipher suite priority and Flash security, be sure to check their advisory page for those new updates. — Corey Nachreiner, CISSP (@SecAdept)

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