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 Web site, 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 Web site, 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 2004. 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 Web site and a trusted Web site 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 Web site, Secunia said. The company advised people not to visit trusted and untrusted Web sites 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 Web site wrote Monday, in response to the Secunia alert.
For protection, the moderator advises people to close all other windows and tabs before accessing a Web site such as a bank or online store that 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.
