Vulnerability Crosses Browser Boundaries

A security researcher has found a flaw in browser scripting that could open a range of products to file stealers.

Charles McCauley, an independent researcher, on Tuesday published proof-of-concept code that demonstrates how attackers could lure users into entering text into a seemingly secure electronic form, only to have the data stolen as they type.

A report from the French Security Incident Reporting Team (FrSIRT) describes the possible scenario: "This flaw could be exploited by remote attackers to trick users into uploading arbitrary files from a vulnerable or malicious host by convincing them to visit a specially-crafted Web page and perform certain actions (e.g. type into a text field) that will cause an arbitrary file to be inadvertently uploaded."

Attackers could use the flaw to steal the directory path of secure files and then upload them, according to the vulnerability reports.

The exploit is unusual because it takes advantage of a flaw that exists in both JavaScript, which is used by four Mozilla browsers, and Active Scripting, which is used in Internet Explorer. Both tools contain a design error that lets a script cancel certain keystroke events when users are entering text, and this error can be repurposed to let the attacker steal the user's keystrokes, McCauley reports.

Any browser that uses JavaScript or Active Scripting, including current and beta versions of IE as well as Mozilla's Firefox for Windows, Linux, and Mac OS X, and its next-generation SeaMonkey, are vulnerable.

Most vulnerability reports have listed the threat as medium to moderate, since a user would have to type a great deal of text into the field in order to reveal secure directory information. For example, the user would have to type the entire data path to a file before the attacker could access the directory.

Neither Microsoft nor Mozilla has issued a patch for the bug.

— Tim Wilson, Site Editor, Dark Reading

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