Specially Crafted Attachments Can Crack Exchange Servers

Severity: High

Summary:

• These vulnerabilities affect: Exchange Server 2007 and 2010
• How an attacker exploits it: By enticing a user to preview a specially crafted email attachment using OWA
• Impact: An attacker can execute code with the restricted privileges of the LocalService account
• What to do: Deploy the appropriate Exchange Server update as soon as possible, or let Windows Automatic Update do it for you

Exposure:

Microsoft Exchange is one of the most popular email servers used today. It includes many advanced features and capabilities. One such feature, called WebReady Document Viewing, allows your email users to preview attached documents as web pages. Exchange leverages Oracle’s Outside In technology to parse these documents and provide these previews.

According to today’s bulletin, Exchange suffers from two vulnerabilities related to Oracle’s Outside In; a remote code execution flaw and a Denial of Service (DoS) issue. Both vulnerabilities have to do with how WebReady Document Viewing parses certain files when showing previews. By enticing one of your web-based email users to preview an email with a specially crafted attachment, an attacker can exploit the worst of these flaws to execute code directly on your Exchange server. Luckily, the code only runs with LocalService account permissions, which has very limited privileges.

Also, this attack only works against victims who check and preview mail using Exchange’s Outlook Web App (OWA). If your users only get email from Exchange using email clients, and you don’t enable OWA, attackers may not be able to leverage this flaw against your server. However, we still recommend Exchange administrators update as soon as possible.

By the way, if this issue seems familiar to you, it’s because it is very similar to a previous Exchange WebReady Document Viewing issue from last year.

Solution Path:

Microsoft has released Exchange updates to correct these vulnerabilities. You should download, test, and deploy the appropriate update as soon as possible, or let Windows Update do it for you. You can find the updates in the “Affected and Non-Affected Software” section of Microsoft’s Exchange bulletin.

UPDATE: At least one of our readers has reported issues when trying to install the Exchange update. Be sure to test before pushing this to production.

For All WatchGuard Users:

Though you can configure 0ur XTM and XCS appliances to strip certain attachments from email, this sort of attack may arrive as many types of attachments, including ones you may want to allow for business. We recommend you apply the patches instead.

Status:

Microsoft has released patches to fix these vulnerabilities.

References:

• MS Security Bulletin MS13-012

This alert was researched and written by Corey Nachreiner, CISSP (@SecAdept).