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 3.6.1 (or 3.5.14), or let Firefox’s automatic update do it for you
Exposure:
Late Tuesday, Mozilla released a Firefox update fixing around 13 (count based on CVE numbers) vulnerabilities in their popular multi-platform web browser. Mozilla rates 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 3.6.10 vulnerabilities below:
- Multiple Dangling Pointer vulnerability (2010-67). A function within Firefox (LookupGetterOrSetter) suffers from a software flaw called a dangling pointer vulnerability. In the past, programmers considered dangling pointer flaws relatively benign, since attackers couldn’t easily exploit them. More recently, researchers have proven this class of flaw quite exploitable. By enticing one of your users to a web page, an attacker can leverage these vulnerabilities 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
- Buffer Overflow Vulnerability in Document.write (2010-65). According to Mozilla, the latest Firefox update fixes a buffer overflow vulnerability in the code responsible for text rendering (document.write). By enticing one of your users to a maliciously crafted web page, 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. As usual, an attacker may gain full control of your users’ computers if they have administrative privileges.
Mozilla Impact rating: Critical
- Typical Memory Corruption Vulnerabilities (2010-64). Mozilla’s update fixes three mostly 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
Mozilla’s alert describes many more vulnerabilities, including more code execution flaws, a few Cross-Site Scripting (XSS) vulnerabilities, and a few certificate and encryption issues. Visit Mozilla’s Known Vulnerabilities page for a complete list of the vulnerabilities that Firefox 3.6.11 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 3.6.11. 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 3.6.1 and 3.5.14, to correct these security vulnerabilities. If you use Firefox in your network, we recommend that you download and deploy version 3.6.11 as soon as possible, or let Firefox’s automatic updater do it for you. If, for some reason, you must remain with Firefox 3.5.x, make sure to upgrade to 3.5.14.
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 3.6.11 to fix these vulnerabilities.
References:
This alert was researched and written by Corey Nachreiner, CISSP.
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