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[Bug 18975] New: registerContentHanlder and registerProtocolHandler open huge security and privacy holes

From: <bugzilla@jessica.w3.org>
Date: Sat, 22 Sep 2012 15:54:02 +0000
To: public-html@w3.org
Message-ID: <bug-18975-2495@http.www.w3.org/Bugs/Public/>

           Summary: registerContentHanlder and registerProtocolHandler
                    open huge security and privacy holes
           Product: HTML WG
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: blocker
          Priority: P2
         Component: HTML5 spec
        AssignedTo: erika.doyle@microsoft.com
        ReportedBy: lmm@acm.org
         QAContact: public-html-bugzilla@w3.org
                CC: mike@w3.org, public-html-wg-issue-tracking@w3.org,

The Custom scheme and content handlers features of
registerProtocolHandler and registerContentHandler open huge security and
privacy holes which are not described in the specification and for which there
is no reliable mitigation such that users of these features could count on.

It's understandable that these are attractive features from the point of view
of the power they put in the hands of developers of new protocols and

The bug is that these features are inadequately specified and the security of
them inadequately analyzed and mitigated.

Here is an incomplete analysis:

These features expand the attack surface for introduction of malware, for
leakage of private information in unanticipated and undisclosed ways. While the
security section alludes to a few of the problems, the mitigations given are
not implementable in a way that a browser-independent web application that
wished to use the features could do so reliably. 

For one small example, registerContentHandler for a new image type might merely
prompt the user for permission to install a new content-type handler, without
clearly identifying that now, all images of that type will be sent to the
handler site as soon as the image is received.  This gives the site that
registers the content handler far more information about the user's activities.
It exacerbates the current difficulties of multiple applications overwriting
the default content handler for various media types, provides for no 'undo'
mechanism for putting back pointers to local interpreters, etc.

As these are intended to be permanent changes to the underlying systems and not
bounded by interpretation within the browser, a web site is now allowed to
affect the permanent operation of the receiver's system. While this might be
thought of as no different from typical installation dialogs, installing new
software on a system usually involves virus and malware scanning, checking
digital signatures of the the installed code and so forth. After a new handler
has been installed, the server of the handler is now part of an attack surface.

Attempting to strengthen the mechanism for preventing malicious overwriting of
legitimate handlers could merely encourage malicious preemptive registration of

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Received on Saturday, 22 September 2012 15:54:03 UTC

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