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Internet Explorer iframe sandbox local file name disclosure
vulnerability
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Yorick Koster, March 2016

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Abstract
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It was found that Internet Explorer allows the disclosure of local file
names. This issue exists due to the fact that Internet Explorer behaves
different for file:// URLs pointing to existing and non-existent files.
When used in combination with HTML5 sandbox iframes it is possible to
use this behavior to find out if a local file exists. This technique
only works on Internet Explorer 10 & 11 since these support the HTML5
sandbox. Also it is not possible to do this from a regular website as
file:// URLs are blocked all together. The attack must be performed
locally (works with Internet zone Mark of the Web) or from a share.

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See also
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- CVE-2016-3321
- MS16-095: Cumulative Security Update for Internet Explorer (3177356)

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Tested versions
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This issue was successfully verified on Internet Explorer 10 and
Internet Explorer 11. The HTML5 sandbox iframes is not available in
older versions of Internet Explorer.

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Fix
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Microsoft released MS16-095 that fixes this vulnerability.

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Details
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https://www.securify.nl/advisory/SFY20160301/internet_explorer_iframe_sandbox_local_file_name_disclosure_vulnerability.html