Firefox 3.6.7 Fixes a Bunch of Drive-by Download Vulnerabilities

21 July, 2010

Summary:

§  These vulnerabilities affect: Firefox 3.6.x and 3.5.x for Windows, Linux, and Macintosh

§  How an attacker exploits it: Typically by enticing one of your users to visit a malicious web page

§  Impact: Various results; in the worst case, an attacker executes code on your user's computer, gaining complete control of it

§  What to do: Upgrade to Firefox 3.6.7 (or 3.5.11), or let Firefox's automatic update do it for you

Exposure:

Today, Mozilla released an advisory describing 16 (count based on CVE number) vulnerabilities in Firefox 3.6.4 (and earlier versions) running on all platforms. Mozilla rates more than half of these vulnerabilities as critical; meaning an attacker can leverage them to execute code and install software without user interaction beyond normal browsing. We summarize three of the most critical Firefox 3.6.4 vulnerabilities below:

§  PNG Image Buffer Overflow Vulnerability (2010-41). The graphics code that helps Firefox handle PNG images suffers from a buffer overflow vulnerability. By enticing one of your users to a web page containing a maliciously crafted image, an attacker can leverage this buffer overflow to either crash Firefox, or to execute malicious code on that user's machine, with that user's privileges. If the user happened to be a local administrator or had root privileges, the attacker would gain total control of the victim's computer.
Mozilla Impact rating: Critical

§  Typical Memory Corruption Vulnerabilities (2010-34). Mozilla's update fixes two unspecified memory "safety" or corruption vulnerabilities, which can at least crash Firefox. Mozilla's alert doesn't say much about these vulnerabilities, other than they lie within Firefox's browser engine. Mozilla presumes that, with enough effort, attackers could exploit some of these memory corruption flaws to run arbitrary code on a victim's computer. To do so, an attacker would first have to trick one of your users into visiting a maliciously crafted web page. If your user took the bait, the attacker could execute malicious code on that user's machine, with that user's privileges. If the user happened to be a local administrator or had root privileges, the attacker would gain total control of the victim's computer. 
Mozilla Impact rating: Critical

§  DOM Attribute Cloning Code Execution Vulnerability (2010-35). The Document Object Model (DOM) is a W3C specification for representing structured documents as objects, in a platform and language neutral manner. Firefox's DOM attribute cloning routine suffers from a code execution vulnerability. By enticing one of your users to a maliciously crafted web page, an attacker can leverage this flaw to either crash Firefox, or to execute malicious code on that user's machine, with that user's privileges. As usual, an attacker may gain full control of your users' computers if they have administrative privileges.

Mozilla's alert describes many more vulnerabilities, including other code execution flaws, Cross-Site Scripting (XSS) or cross-origin vulnerabilities, and spoofing vulnerabilities. Visit Mozilla's Known Vulnerabilities page for a complete list of the vulnerabilities that Firefox 3.6.7 fixes. 

On a related note, some of these vulnerabilities also affect Firefox 3.5.x. If you use 3.5.x, we recommend you move to 3.6.7. However, if you must stay with 3.5.x, Mozilla has also released an update for that legacy version as well.

Solution Path:

Mozilla has released Firefox 3.6.7 and 3.5.11, to correct these security vulnerabilities. If you use Firefox in your network, we recommend that you download and deploy version 3.6.7 as soon as possible. If, for some reason, you must remain with Firefox 3.5.x, make sure to upgrade to 3.5.11.

Note: The latest version of Firefox 3.6.x automatically informs you when a Firefox update is available. We highly recommend you keep this feature enabled so that Firefox receives its updates as soon as Mozilla releases them. To verify that you have Firefox configured to automatically check for updates, click Tools => Options => Advanced tab => Update tab. Make sure that "Firefox" is checked under "Automatically check for updates." In this menu, you can configure Firefox to always download and install any update, or if you prefer, only to inform the user that an update exists.

As an aside, attackers cannot leverage many of these vulnerabilities without JavaScript. Disabling JavaScript by default is a good way to prevent many web-based vulnerabilities. If you use Firefox, we recommend you also install the NoScript extension, which will disable Javascript (and other active scripts) by default.

For All Users:

This attack arrives as normal-looking HTTP traffic, which you must allow through your firewall if your network users need to access the World Wide Web. Therefore, the patches above are your best solution.

Status:

The Mozilla Foundation has released Firefox 3.6.7 to fix these vulnerabilities.

References:

§  Firefox 3.6.7 Release Notes

§  Vulnerabilities Fixed in Firefox 3.6.7

This alert was researched and written by Corey Nachreiner, CISSP.