Severity: High
Summary:
- These vulnerabilities affect: Microsoft Office and related products, including SharePoint
- How an attacker exploits them: Varies. Typically by enticing users to visit malicious web content or open Office documents
- Impact: Many. In the worst case, an attacker can gain 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
Exposure:
Today, Microsoft released three security bulletins that fix a like number of vulnerabilities in Microsoft Office and related products like SharePoint. We summarize these security bulletins below, in order from highest to lowest severity.
- MS13-100: SharePoint Code ExecutionVulnerability
SharePoint Server is Microsoft’s web and document collaboration and management platform. SharePoint, and some of its related components, suffer from an unspecified remote code execution flaw having to do with how it parses specially crafted page content. If an authenticated attacker can upload specially crafted content to your SharePoint server, he could leverage this flaw to execute code on that server with the W3WP (w3wp.exe) service account's privileges.
Unfortunately, Microsoft's alert doesn't go into detail about the privileges associated with the W3WP services account. However, we've found that w3wp.exe often runs as a child process under svchost.exe, which runs with local SYSTEM privileges by default; potentially making this a complete system compromise. However, Microsoft assigns this particular flaw an Important severity rating, probably because the attacker needs valid SharePoint credentials to exploit it.
Microsoft rating: Important
- MS13-104: Office Access Token Hijacking Flaw
When you login to an Office or Sharepoint server, the server verifies your credentials and then produces an access token, which allows you to continue accessing the server for a limited period of time. Office suffers from an unspecified flaw having to do with how it handles documents hosted on web sites. If an attacker can entice you into opening an Office document hosted on a malicious site, he could exploit this flaw to gain access to your access token, and then may be able to leverage that token to hijack your SharePoint of Office server sessions.
Microsoft rating: Important
- MS13-106 : Office ASLR Bypass Vulnerability
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. One of the shared components that ships with Office products doesn't enable ASLR protection. This means attackers can leverage this particular component to bypass Windows' ASLR protection features. This flaw alone doesn't allow an attacker to gain access to your Windows computer. Rather, it can help make other memory corruption vulnerabilities easier to exploit. Since Internet Explorer (IE) loads this component, it's particularly useful for attackers. This update fixes the ASLR bypass hole. If you'd like more details about this fix, and how it helps your overall Windows security, see this Microsoft blog post. Though Microsoft only gives this their medium severity rating, we recommend you apply the update quickly.
Microsoft rating: Important
As an aside, Microsoft also released a security bulletin (MS03-103) describing a flaw that primarily affects developers and organizations that specifically use the ASP.NET SignalR library. If you happen to use the ASP.NET SignalR library, do know it suffers from a relatively minor cross-site scripting (XSS) vulnerability, and you should update.
Solution Path:
Microsoft has released Office-related patches that correct all of these vulnerabilities. You should download, test, and deploy the appropriate updates throughout your network as soon as possible. If you choose, you can also let Windows Update automatically download and install these updates for you.
The links below point directly to the “Affected and Non-Affected Software” section of each bulletin, where you can find all of Microsoft's update links: