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Programming flaws in Firefox and Opera allow attackers to hide an entire malicious web page in a clickable link, which could fool a victim into handing over passwords and other sensitive info.

Usually, phishing attacks rely on tricking victims into visiting sites designed by criminals to masquerade as banks and online stores, which makes it easy to steal logins and bank account details when they try to use the bogus pages.

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However, this requires finding somewhere to host the counterfeit sites, which often end up taken down by hosting companies and the authorities or blocked by filters.

Instead, the malicious web pages can store in data URIs (uniform resource identifiers) which stuff the web code into a handy string that when clicked on, instructs the browser to unpack the payload and present it as a page.

Cyber Security

It negates the need to find somewhere to secrete your malicious page, and once shortened using a service such as TinyURL, the URI can shrink down into a small URL perfect for passing around social networks, online chats and email. The only catch is the cyber criminals may need to set up a server to receive data from victims.

It’s a technique already documented by researchers Billy Rios and Nathan McFeters, but now Henning Klevjer, an information security student at the University of Oslo in Norway, has revisited the attack method in his paper, “Phishing by data URI.”

Typically an attacker would first create a standalone web page, probably using content scraped off the legitimate site it seeks to mimic before making an encoded page and embedding it into a data URI.

URI-based attacks, previously documented by Rios and McFeters, are a part of an attack on Microsoft’s Internet Explorer 6 and 7. Klevjer’s research expands on this basic theme and gives it a modern twist.

Google’s Chrome browser blocks redirection to data URIs, and other browsers have limits on the volume of data that can pack into URIs. Klevjer created a 26KB attack page that failed to load in Internet Explorer, but worked on Firefox and Opera.

As well as getting around the need to find a home for malicious web pages, the data URI trick can sidestep traditional scam defenses, such as web filtering. Data URIs may also contain a potentially malicious Java applet, a major concern following last week’s Java-related security issue.

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