Firefox flaw reopens old wounds

A seven-year-old flaw that could let an attacker place malicious content on trusted websites has resurfaced in the most recent Firefox browser, Secunia has warned.

The flaw, which also affects some other Mozilla Foundation programs, lies in the way the software handles frames, which are a way of showing web content in separate parts of the browser window. The applications don't check whether the frames displayed in a single window all originate from the same website, Secunia said in an advisory on Monday. Firefox 1.x, Mozilla 1.7.x and Camino 0.x versions are vulnerable to the flaw, the security monitoring company said.

As a result, an attacker could insert content into a frame on a trusted website, Secunia said. Account holders who believe they are interacting with a frame belonging to an online bank could be tricked into giving up personal information or downloading malicious code, for example. Secunia rated the issue "moderately critical".

The same "frame injection" vulnerability in Mozilla's browsers was detailed by Secunia in July of last year. At the time, it did not affect the most recent versions of the applications.

For a spoofing attempt to work, a surfer would need to have both the attacker's website and a trusted website open in different windows. A click on a link on the malicious site would then display the attacker's content in a frame on the trusted website, Secunia said. The company advised people not to visit trusted and untrusted websites at the same time.

The Mozilla Foundation is investigating the Secunia report, a representative for the organisation said.

The vulnerability has not been exploited, a moderator of a support forum on the Mozilla website wrote on Monday, in response to the Secunia alert.

For protection, the moderator advises people to close all other windows and tabs before accessing a website such as a bank or online store which requires them to type in personal data.

With its initial release last fall, Firefox has demonstrated that the mature web browser market dominated by Microsoft's Internet Explorer can be shaken up. IE has begun to see its market share dip slightly - a first in a number of years.

Joris Evers writes for CNET News.com