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 3.6.13 (or 3.5.16), or let Firefox’s automatic update do it for you
Exposure:
Last week, Mozilla released a Firefox update fixing 13 (count based on CVE number) vulnerabilities in their popular multi-platform web browser. Mozilla rates most 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 3.6.12 vulnerabilities below:
- Integer Overflow Vulnerability in Javascript Array (2010-81). A javascript array (specifically NewIdArray) in Firefox suffers from an integer overflow vulnerability that can cause a memory buffer overflow. 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. 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 - Document.write() Buffer Overflow Vulnerability (2010-75). According to Mozilla, one of the javascript methods used to write text to a page (document.write) suffers from a buffer overflow vulnerability. By enticing one of your users to a web page containing specially crafted javascript, 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 - Three Memory Corruption Vulnerabilities (2010-74). Mozilla’s update fixes three unspecified memory “safety” related 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 critical vulnerabilities, most of which allow attackers to execute code simply by enticing you to a malicious web page. Visit Mozilla’s Known Vulnerabilities page for a complete list of the vulnerabilities that Firefox 3.6.13 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 3.6.13. 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 3.6.13 and 3.5.16, to correct these security vulnerabilities. If you use Firefox in your network, we recommend that you download and deploy version 3.6.13 as soon as possible. If, for some reason, you must remain with Firefox 3.5.x, make sure to upgrade to 3.5.16.
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 3.6.13 to fix these vulnerabilities.
References:
This alert was researched and written by Corey Nachreiner, CISSP.
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