A security loophole in Mozilla and Firefox browser could be used to spoof the URL displayed in the address bar, SSL certificate and status bar. The vulnerability also affects Opera and Konqueror and stems from a flawed IDN (International Domain Name) implementation within the browsers.

The bug could be exploited by registering domain names with certain international characters - which look like other commonly-used characters - in order to hoodwink users into believing they on a different, trusted site. As such, the bug creates a new wheeze for phishing attacks. For Germans to use national German characters in ".de" domains, for example, is one thing, but the use of national characters has been extended to the international domain space (.com, .net an .org) and extends the scope for confusion.

Thomas Kristensen, CTO at Secunia told El Reg: "This issue is not a traditional vulnerability, but a serious security issue which is caused by an inappropriate implementation of IDN."

"We have all heard about the "problems" with "o" that looks like "0" or "l" and "1", allowing people to register "MlCR0S0FT.com" and abusing that to trick people. Using IDN which support Unicode characters gives the phishers and scamsters thousands of more characters to play around with, some resemble "normal" characters to the point where not even the trained and paranoid eye will spot the difference, " he said.

The bug has been confirmed in Mozilla 1.7.5, Firefox 1.0, Konqueror 3.2.2 and Opera 7.54. Other versions may also be affected, Secunia reports. Internet Explorer users are in the clear from this one, although subject to flaws that have a similar effect. You can check if your browser is affected using Secunia's test.

Secunia advises users not to follow links from untrusted sources and to manually type in the URL they wish to visit in the address bar as workaround prior to the availability of more comprehensive fixes. ®

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