Two new product security patches from Microsoft target a number of critical security flaws in the Outlook Express e-mail application and Internet Explorer Web browser.
The bulletins, MS03-014 and MS03-015, were released Wednesday by the Redmond, Washington, software maker and describe a variety of security flaws that could give remote attackers access to data stored on machines running the vulnerable applications.
Two versions of Outlook Express, 5.5 and 6.0, contain a vulnerability in a component called the MHTML URL Handler. The vulnerability makes it possible for an attacker to use a URL (Uniform Resource Locator) to run scripts on a remote user's machine, possibly reading files or launching applications on that host machine, provided the user knew where the files were located, Microsoft said. Outlook users would have to be tricked into clicking on the URL, possibly receiving it in an e-mail message, Microsoft said.
MHTML, or MIME Encapsulation of Aggregate HTML, is an Internet standard that governs the transmission of HTML (Hypertext Markup Language) content in e-mail message bodies. The MHTML URL Handler enables Outlook Express to format HTML content for e-mail messages, rendering files of any type as HTML, the language used to format and display information on the Web.
A flaw in an Outlook Express component used to display MHTML format pages allows non-MHTML pages to be displayed as HTML. Attackers could embed a script in a text format file, for example, that would be executed when displayed as HTML, Microsoft said.
Combined with other vulnerabilities patched in an earlier cumulative patch for Internet Explorer, MS03-004, the Outlook Express vulnerability reported Wednesday could enable an attacker to load a file onto a user's system then exploit it, Microsoft said.
Any files or applications that were executed would run in the Local Computer Zone, meaning that fewer restrictions would be placed on the malicious code than if it were run in the Internet Zone, the company said.
Microsoft urged customers to apply the MS03-014 patch, but said that customers using the Outlook Express 6.0 or Outlook 2002 e-mail clients in their default configuration or patched versions of the Outlook 98 and 2000 clients would be protected from attacks sent via e-mail.
In the case of the Internet Explorer Web browser (IE), Microsoft issued a cumulative patch, MS03-015, that covers four previously undisclosed product vulnerabilities affecting IE versions 5.01 and 6.0.
A buffer overrun in an IE component called Urlmon.dll, a flaw in IE's rendering of third-party files and in the way IE handles so-called "modal dialogs," which ask the user to make a decision, were all rated "critical" by Microsoft.
A fourth vulnerability in a file upload control that enables users to upload a file to a Web site from a local computer was called "moderate" by Microsoft.
In all cases, attackers could exploit the vulnerabilities by embedding attacks in specially crafted Web pages. Users could be lured into viewing the attack pages by clicking on a URL embedded in an e-mail message or planted on another Web site, Microsoft said.
In some cases, users running vulnerable versions of IE would need to click a separate link to trigger the vulnerability once they had visited the page.
In the case of the Urlmon.dll vulnerability and the modal dialog vulnerability, however, just visiting an attacker's page would be sufficient to launch an attack.
In the Urlmon.dll vulnerability, attackers could crash IE, placing and running their own malicious code on the victim's machine. In the modal dialog vulnerability, attackers could access files on the user's machine, provided that the attacker knew the location and names of those files.
Microsoft recommended that administrators apply the MS03-015 patch immediately, saying that it supersedes an earlier cumulative IE patch, MS03-004.