Mozilla Firefox Released

Tuesday July 31st, 2007

Mozilla Firefox has been released. This browser upgrade fixes two security flaws, which are detailed in the Firefox section of the Mozilla Foundation Security Advisories page.

The more serious flaw involves Firefox not percent-encoding spaces and double quotes in URLs passed to helper applications, which can allow malicious webpages to open programs with potentially dangerous command line parameters. The other vulnerability is a privilege elevation bug involving extensions, which was accidentally introduced in Firefox

The URL protocol handling flaw is a similar class of exploit to the firefoxurl:// URL vulnerability, which was fixed with the release of Firefox In the original firefoxurl:// exploit, an attacker could use Microsoft Internet Explorer to launch Firefox with malicious command line parameters. In the flaw fixed in Firefox, Firefox is used as the attack vector to start other applications with dangerous arguments. The exploit could be extended to execute any program in a known location, possibly passing dangerous command line parameters.

Whether or not it's Firefox's responsibility to ensure that data passed to external applications is (relatively) safe is a matter for debate. When the original firefoxurl:// URL vulnerability was discovered, Microsoft claimed that IE was not at fault. However, as Mozilla maintained at the time that the blame lay with IE, it would have been hypocritical not to fix the similar issue in Firefox. The Mozilla Security Blog post about the URL protocol handling flaw states that "defense in depth is the best way to protect people" (although that weblog post says that only Windows is affected, discussion in bug 389106 indicates that Linux and Mac OS X may also be vulnerable).

Firefox prompts the user before launching most helper applications and shows the command line parameters, so users of vulnerable versions would receive some warning of an attack (though only the savvy are likely be knowledgeable enough to distinguish between safe and malicious command lines). However, some protocols related to email and newsgroups (specifically, mailto, news, nntp and snews) do not prompt the user before launching an external application, so vulnerable mail and newsgroups applications could be exploited with minimal user intervention (Thunderbird and earlier is one such application, due to its variant of the firefoxurl:// problem).

More details about Firefox can be found in the Firefox Release Notes. The new version can be downloaded from the Firefox product page. Existing Firefox 2 users with the software update feature enabled (it's on by default) will be prompted to upgrade. Equivalent releases of Thunderbird (both 2 and 1.5) and SeaMonkey are expected soon.

#1 not really the reason

by asa <>

Tuesday July 31st, 2007 1:52 PM

You are replying to this message

You said, "as Mozilla maintained at the time that the blame lay with IE, it would have been hypocritical not to fix the similar issue in Firefox."

I'd just like to point out that at the time we were calling on IE to fix this in their code, it was assumed (wrongly) that we had in the past suffered from this same problem and fixed it in our code. Our reason for fixing it then was not to avoid the appearance of hypocrisy, but because it's the right thing to do to protect users. Your phrasing suggests that you think Mozilla was somehow pressured by concerns over maintaining appearances or something like that and I just wanted to make it clear that was not the case.

- A