Security researchers last week said that Mac OS X and Linux operating systems are probably at risk of a new kind of web-based security vulnerability that Microsoft has patched Windows to address.

Nathan McFeters, a researcher who has been studying the problem, will speak this week at the Toorcon hacking conference, in San Diegos. He hopes to present more details on how other Unix-based operating systems - such as Linux and Mac OS X - may be susceptible to URI (uniform resource identifier) protocol handler flaws.

In an interview, McFeters said that he had not yet found a way to run unauthorised code on Unix-based operating systems, but that he and his fellow researchers had discovered a number of issues that looked as though they could be grounds for further research.

The problem McFeters and others have been researching over the past few months has to do with the URI protocol handling technology, used to launch programs from within web browsers. Probably the best known of these protocols is mailto, which is used to launch the mail client from within the internet browser.

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But any software developer can register their own application with the operating system. This leads to a somewhat risky state of affairs as programs are launched within the browser, sometimes without proper checks on the way they are being executed.

To date, hackers have found ways to run unauthorised software on the PC by sneaking commands into specially crafted web links that use the URI protocols of several well-known applications. Microsoft had originally said that it was up to software developers to make sure their programs check the links so that they don't include malicious code, but this week it agreed to put some checks within the Windows operating system as well.

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McFeters, a security researcher with Ernst & Young Global, says that often these protocols are registered unnecessarily and with little thought given to security. Even if it can't be used to install unauthorised software, a poorly designed URI protocol registration can end up giving attackers access to data and applications that they shouldn't be able to see, he added.

Last month, McFeters and Researcher Billy Rios showed how a flaw in Google's Picasa software could give an attacker access to any Picasa photos stored on the victim's hard drive. And URI protocol handler flaws have also been found in Adobe, Firefox and Outlook Express.

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Secunia ApS Chief Technology Officer Thomas Kristensen agreed that the URI protocol handler problems will probably turn up on Linux and Mac OS X. "There is absolutely a chance that similar issues could exist on those platforms," he said.

He also agreed with McFeters that too many programs needlessly register protocols and urged corporate and commercial software developers to reduce their reliance on this technique.

"When people are designing the applications they're simply not thinking about how secure the environment is and how it's really working," he said.