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Date: Fri, 7 Feb 2014 12:49:00 -0500 (EST)
From: cve-assign@...re.org
To: djorm@...hat.com
Cc: cve-assign@...re.org, oss-security@...ts.openwall.com
Subject: Re: CVE request: multiple issues in Apache Cordova/PhoneGap

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> Multiple issues have been reported in Apache Cordova:
> 
> http://packetstormsecurity.com/files/124954/apachecordovaphonegap-bypass.txt

We have been looking at this report, and have this initial response.

First, the CVE assignments are based on the NDSS 2014 paper itself:

  http://www.internetsociety.org/ndss2014/programme#session3
  http://www.cs.utexas.edu/~shmat/shmat_ndss14nofrak.pdf

not on the apachecordovaphonegap-bypass.txt summary. Although the
summary presumably covers the most important points about the authors'
research and solutions, it doesn't focus on software mistakes in the
same way that CVE does. The NDSS paper mentions a vulnerability in
Android, framework vulnerabilities (in Apache Cordova and possibly
other frameworks), and vulnerabilities in individual apps.


Page 5 of the NDSS paper says:

> On Android prior to API level 17, these interfaces are generically
> insecure. Malicious JavaScript executing inside WebView can use the
> Java reflection API to invoke any method of any Java object exposed
> via 'addJavascriptInterface' and take control over the local side of
> the application

This Android vulnerability is CVE-2012-6636. The available information
about the point of original disclosure is
http://50.56.33.56/blog/?p=314 and we don't happen to know if the
researcher has a personal domain name for 50.56.33.56 that should be
used instead.

In this p=314 post, the researcher says "Prior to Android 4.2, if an
application uses the addJavascriptInterface and allows an attacker to
control the content rendered in a WebView, then an attacker can take
control over the parent application regardless of the type of
interface exposed." This seems to be a different finding than in the
referenced
http://www.cis.syr.edu/~wedu/Research/paper/webview_acsac2011.pdf
paper. (Yes, webview_acsac2011.pdf can have CVE-2011-#### ID
assignments but we are not working on that at the moment.)

Incidentally, several other researchers are apparently working on
reports about use of addJavascriptInterface in individual Android
apps. For example, see the "Threat Report of Android App" .png file
within the blog.trustlook.com reference in CVE-2014-1670. That
reference mentions "hundreds of vulnerable apps."


Page 4 of the NDSS paper says:

> in our threat model we consider malicious advertisers, but not
> malicious ad brokers. The latter are trusted by app developers and,
> critically, their Web code is indistinguishable from the app's own
> code as far as the SOP is concerned.

This seems to be a useful threat model for the research goals, but is
not necessarily a threat model that applies directly to CVE
assignment. Specifically, a hybrid application framework could take
the position that malicious advertisers are entirely a broker's
problem. In other words, an app could be offered to users with a
statement of "We use these ad brokers. If you do not trust these ad
brokers and all of their advertisers, you should not install this
app." (Admittedly, with current advertising models, this statement
might be essentially useless and might never occur.) The implication
is that lack of protection against malicious advertisers is not
fundamentally a software mistake and, by itself, does not qualify for
a CVE assignment. To have a CVE assignment, there needs to be an
implementation error in the mechanism for protection against malicious
advertisers.


Page 7 of the NDSS paper says

> they allow JavaScript on the Web side to choose a bridge via
> 'setNativeToJsBridgeMode' and 'setJsToNativeBridgeMode' functions.
> These functions are not intended to be called directly by hybrid apps,
> since apps are supposed to access the framework only through the
> public API, but they are not protected by the SOP.

Here, the unintended availability of function calls might be
considered a vulnerability, but it is not really independent of the
existence of a specific vulnerable bridge. If no bridge were vulnerable,
ability to call setNativeToJsBridgeMode and setJsToNativeBridgeMode
might be considered a non-security bug.

> Therefore, a malicious script is free to invoke them in order to
> select a vulnerable bridge. Consequently, even if some bridges are
> secure, a single vulnerable bridge is sufficient to bypass all of the
> framework's defenses. Availability of bridges varies from version to
> version even within the same framework

The "varies from version to version" observation, with no further
details, complicates the CVE assignment process. The two Apache
Cordova CVE-2014-#### assignments below apply to all event-based
bridges that can be attacked in version 3.3.0. If anyone wants to
mention event-based bridges that could be attacked in previous
versions, but cannot be attacked (or do not exist at all) in 3.3.0,
additional CVE assignments are possible.

Page 10 of the NDSS paper says:

> For event-based bridges only, PhoneGap on Android attempts to enforce
> the NoBridge property.

Also, page 7 of the NDSS paper says:

> Exploiting event-based bridges ... some analyses mistakenly concluded
> that event-based bridges cannot be exploited by malicious JavaScript

> This conclusion is false. Modified, malicious clones of the
> framework's JavaScript library can access local resources via
> event-based bridges even when confined in an iframe.
> 
> First, if the malicious script inside an iframe cannot receive
> synchronization events from the framework's local half, it can
> simply block for a predefined interval ...

Use CVE-2014-1881 for this first issue.


> Second, even if the framework's utility objects are not
> visible from an iframe, the main JavaScript objects implementing the
> bridge are available, and malicious code can access them directly.

Use CVE-2014-1882 for this second issue.


> Before version 2.6, PhoneGap on Android used a WebView callback
> 'shouldOverrideUrlLoading' to intercept the loading of foreign-origin
> content. This callback is not invoked for iframe fetches or
> XMLHttpRequests. Therefore, this defense cannot prevent a hybrid app
> from loading unauthorized content as, for example, an ad in an iframe.
> PhoneGap 2.6, released on April 9, 2013, uses the
> 'shouldInterceptRequest' callback which correctly intercepts the
> loading of iframes. This callback is only supported by Android API 11
> or later.

Use CVE-2014-1883. A CVE-2013-#### ID was considered, but there didn't
seem to be an obvious disclosure of the issue in 2013 on the
https://github.com/phonegap/phonegap/blob/2.6.0/changelog page.


> Windows Phone 7 and 8. PhoneGap installs a handler for the browser's
> navigation event and checks the whitelist before allowing navigation.
> This event is not triggered for iframe fetches and XMLHttpRequests.
> Therefore, this defense fails to guarantee NoLoad.

Use CVE-2014-1884.


> All tested versions of PhoneGap for Android, including 2.6,
> incorrectly match intercepted URLs against the whitelist. PhoneGap
> uses Java's regular expression engine and anchors the expression for
> each whitelisted domain only at the beginning, but not the end

This one is clearly an implementation error and is assigned
CVE-2012-6637 for the
http://labs.mwrinfosecurity.com/blog/2012/04/30/building-android-javajavascript-bridges/
reference.


> The 'stringByEvaluatingJavaScriptFromString' and
> 'WebBrowser.InvokeScript' functions, used by the framework's local
> half on iOS and Windows Phone, respectively, to inject JavaScript into
> browsers, execute it in the main frame, not the iframe that invoked
> the bridge.

We currently don't know whether to classify this as an implementation
error or something closer to "known behavior." This behavior does not
seem to be referenced in the apachecordovaphonegap-bypass.txt summary.

As far as we can tell, items 4 and 5 in
apachecordovaphonegap-bypass.txt are usability problems, not security
problems. In item 4, the Same Origin Policy violation seems to be
entirely in the direction of blocking too much.


> Examples of vulnerable PhoneGap apps include ForzeArmate

Use CVE-2014-1885.


> the Edinburgh by Bus app

Use CVE-2014-1886.


> DrinkedIn BarFinder

Use CVE-2014-1887.


(Yes, we realize that it may not be especially important to have CVE
assignments for these three examples, given that potentially hundreds
of similar examples may have been provided.)


> HTTP/HTTPS is ignored when checking URLs against the white list. A
> network attacker can thus downgrade connections from HTTPS to HTTP and
> inject malicious scripts into whitelisted origins.

There is no CVE assignment for this. Although distinguishing between
HTTP and HTTPS is important, addressing this would probably be best
considered a security enhancement, not a vulnerability fix.

> PhoneGap on iOS only allows domain names to be specified in the
> whitelist file, but not HTTP/HTTPS schemes. This prevents the app
> creator from specifying that certain domains should be loaded only
> over HTTPS, which is a very important property

There is no CVE assignment for this. Extending the format of the
whitelist file would be considered a security enhancement.

> out of 7,167 hybrid PhoneGap apps in our study, 2,124 whitelist all
> domains and would have been vulnerable to fracking even if PhoneGap's
> implementation of whitelisting had been correct.

There is no list of apps and thus we are not exploring the possibility
of assigning 2124 CVE IDs.

> PhoneGap on BlackBerry does not take advantage of this facility and
> enforces NoLoad rather than NoBridge

There is no CVE assignment for this. Use of preferable
platform-specific capabilities, wherever available, would probably be
best considered a security enhancement.

> Windows Phone 7.1 has a single permission for all sensors (ID CAP
> SENSORS). If a hybrid app requests this permission and exposes it to
> untrusted Web content, the latter will be able to access any sensor on
> the device.

There is no CVE assignment for this. Extending this permission model
would be considered a security enhancement.

> The key idea behind NoFrak is that all accesses to bridges from the
> Web side must be authenticated by unforgeable capability tokens.

There is no CVE assignment for "older versions do not use capability
tokens" because that would focus too strongly on a solution instead of
the vulnerabilities.

- -- 
CVE assignment team, MITRE CVE Numbering Authority
M/S M300
202 Burlington Road, Bedford, MA 01730 USA
[ PGP key available through http://cve.mitre.org/cve/request_id.html ]
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