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https://wwws.nightwatchcybersecurity.com/2016/10/04/advisory-cve-2016-5348-2/
Summary
Android devices can be crashed remotely forcing a halt and then a soft
reboot by a MITM attacker manipulating assisted GPS/GNSS data provided
by Qualcomm. This issue affects the open source code in AOSP and
proprietary code in a Java XTRA downloader provided by Qualcomm. The
Android issue was fixed by in the October 2016 Android bulletin.
Additional patches have been issued by Qualcomm to the proprietary
client in September of 2016. This issue may also affect other
platforms that use Qualcomm GPS chipsets and consume these files but
that has not been tested by us, and requires further research.
Background – GPS and gpsOneXtra
Most mobile devices today include ability to locate themselves on the
Earth’s surface by using the Global Positioning System (GPS), a system
originally developed and currently maintained by the US military.
Similar systems developed and maintained by other countries exist as
well including Russia’s GLONASS, Europe’s Galileo, and China’s Beidou.
The GPS signals include an almanac which lists orbit and status
information for each of the satellites in the GPS constellation. This
allows the receivers to acquire the satellites quicker since the
receiver would not need to search blindly for the location of each
satellite. Similar functionality exists for other GNSS systems. In
order to solve the problem of almanac acquisition, Qualcomm developed
the gpsOneXtra system in 2007 (also known as IZat XTRA Assistance
since 2013). This system provides ability to GPS receivers to download
the almanac data over the Internet from Qualcomm-operated servers. The
format of these XTRA files is proprietary but seems to contain current
satellite location data plus estimated locations for the next 7 days,
as well as additional information to improve signal acquisition. Most
Qualcomm mobile chipsets and GPS chips include support for this
technology. A related Qualcomm technology called IZat adds ability to
use WiFi and cellular networks for locations in addition to GPS.
Background – Android and gpsOneXtra Data Files
During our network monitoring of traffic originating from an Android
test device, we discovered that the device makes periodic calls to the
Qualcomm servers to retrieve gpsOneXtra assistance files. These
requests were performed almost every time the device connected to a
WiFi network. As discovered by our research and confirmed by the
Android source code, the following URLs were used:
http://xtra1.gpsonextra.net/xtra.bin
http://xtra2.gpsonextra.net/xtra.bin
http://xtra3.gpsonextra.net/xtra.bin
http://xtrapath1.izatcloud.net/xtra2.bin
http://xtrapath2.izatcloud.net/xtra2.bin
http://xtrapath3.izatcloud.net/xtra2.bin
WHOIS record show that both domains – gpsonextra.net and izatcloud.net
are owned by Qualcomm. Further inspection of those URLs indicate that
both domains are being hosted and served from Amazon’s Cloudfront CDN
service (with the exception of xtra1.gpsonextra.net which is being
served directly by Qualcomm). On the Android platform, our inspection
of the Android source code shows that the file is requested by an
OS-level Java process (GpsXtraDownloader.java), which passes the data
to a C++ JNI class
(com_android_server_location_GnssLocationProvider.cpp), which then
injects the files into the Qualcomm modem or firmware. We have not
inspected other platforms in detail, but suspect that a similar
process is used. Our testing was performed on Android v6.0, patch
level of January 2016, on a Motorola Moto G (2nd gen) GSM phone, and
confirmed on a Nexus 6P running Android v6.01, with May 2016 security
patches. Qualcomm has additionally performed testing on their
proprietary Java XTRA downloader client confirming this vulnerability.
Vulnerability Details
Android platform downloads XTRA data files automatically when
connecting to a new network. This originates from a Java class
(GpsXtraDownloader.java), which then passes the file to a C++/JNI
class (com_android_server_location_GnssLocationProvider.cpp) and then
injects it into the Qualcomm modem.
The vulnerability is that both the Java and the C++ code do not check
how large the data file actually is. If a file is served that is
larger than the memory available on the device, this results in all
memory being exhausted and the phone halting and then soft rebooting.
The soft reboot was sufficient to recover from the crash and no data
was lost. While we have not been able to achieve remote code execution
in either the Qualcomm modem or in the Android OS, this code path can
potentially be exploited for such attacks and would require more
research.
To attack, an MITM attacker located anywhere on the network between
the phone being attacked and Qualcomm’s servers can initiate this
attack by intercepting the legitimate requests from the phone, and
substituting their own, larger files. Because the default Chrome
browser on Android reveals the model and build of the phone (as we
have written about earlier), it would be possible to derive the
maximum memory size from that information and deliver the
appropriately sized attack file. Possible attackers can be hostile
hotspots, hacked routers, or anywhere along the backbone. This is
somewhat mitigated by the fact that the attack file would need to be
as large as the memory on the phone.
The vulnerable code resides here – (GpsXtraDownloader.java, lines 120-127):
connection.connect()
int statusCode = connection.getResponseCode();
if (statusCode != HttpURLConnection.HTTP_OK) {
if (DEBUG) Log.d(TAG, “HTTP error downloading gps XTRA: “ + statusCode);
return null;
}
return Streams.readFully(connection.getInputStream());
Specifically, the affected code is using Streams.readFully to read the
entire file into memory without any kind of checks on how big the file
actually is.
Additional vulnerable code is also in the C++ layer –
(com_android_server_location_GnssLocationProvider.cpp, lines 856-858):
jbyte* bytes = (jbyte *)env->GetPrimitiveArrayCritical(data, 0);
sGpsXtraInterface->inject_xtra_data((char *)bytes, length);
env->ReleasePrimitiveArrayCritical(data, bytes, JNI_ABORT);
Once again, no size checking is done. We were able to consistently
crash several different Android phones via a local WiFi network with
the following error message:
java.lang.OutOfMemoryError: Failed to allocate a 478173740 byte
allocation with 16777216 free bytes and 252MB until OOM
at java.io.ByteArrayOutputStream.expand(ByteArrayOutputStream.java:91)
(It should be noted that we were not able to consistently and reliable
achieve a crash in the C++/JNI layer or the Qualcomm modem itself)
Steps To Replicate (on Ubuntu 16.04)
1. Install DNSMASQ:
sudo apt-get install dnsmasq
2. Install NGINX:
sudo apt-get install nginx
3. Modify the /etc/hosts file to add the following entries to map to
the IP of the local computer (varies by vendor of the phone):
192.168.1.x xtra1.gpsonextra.net
192.168.1.x xtra2.gpsonextra.net
192.168.1.x xtra3.gpsonextra.net
192.168.1.x xtrapath1.izatcloud.net
192.168.1.x xtrapath2.izatcloud.net
192.168.1.x xtrapath3.izatcloud.net
4. Configure /etc/dnsmasq.conf file to listed on the IP:
listen-address=192.168.1.x
5. Restart DNSMASQ:
sudo /etc/init.d/dnsmasq restart
6. Use fallocate to create the bin files in “/var/www/html/”
sudo fallocate -s 2.5G xtra.bin
sudo fallocate -s 2.5G xtra2.bin
sudo fallocate -s 2.5G xtra3.bin
7. Modify the settings on the Android test phone to static, set DNS to
point to “192.168.1.x”. AT THIS POINT – Android will resolve DNS
against the local computer, and serve the GPS files from it.
To trigger the GPS download, disable WiFi and enable Wifi, or
enable/disable Airplane mode. Once the phone starts downloading the
files, the screen will go black and it will reboot.
PLEASE NOTE: on some models, the XTRA file is cached and not retrieved
on every network connect. For those models, you may need to reboot the
phone and/or follow the injection commands as described here. You can
also use an app like GPS Status and ToolboxGPS Status and Toolbox.
The fix would be to check for file sizes in both Java and native C++ code.
Mitigation Steps
For the Android platform, users should apply the October 2016 Android
security bulletin and any patches provided by Qualcomm. Please note
that as per Qualcomm, the patches for this bug only include fixes to
the Android Open Source Project (AOSP) and the Qualcomm Java XTRA
downloader clients. Apple and Microsoft have indicated to us via email
that GPS-capable devices manufactured by them including iPad, iPhones,
etc. and Microsoft Surface and Windows Phone devices are not affected
by this bug. Blackberry devices powered by Android are affected but
the Blackberry 10 platform is not affected by this bug. For other
platforms, vendors should follow guidance provided by Qualcomm
directly via an OEM bulletin.
Bounty Information
This bug has fulfilled the requirements for Google’s Android Security
Rewards and a bounty has been paid.
References
Android security bulletin: October 2016
CERT/CC tracking: VR-179
CVE-ID: CVE-2016-5348
Google: Android bug # 213747 / AndroidID-29555864
CVE Information
As provided by Qualcomm:
CVE: CVE-2016-5348
Access Vector: Network
Security Risk: High
Vulnerability: CWE-400: Uncontrolled Resource Consumption (‘Resource
Exhaustion’)
Description: When downloading a very large assistance data file, the
client may crash due to out of memory error.
Change summary:
check download size ContentLength before downloading data
catch OOM exception
Credits
We would like to thank CERT/CC for helping to coordinate this process,
and all of the vendors involved for helpful comments and a quick
turnaround. This bug was discovered by Yakov Shafranovich, and the
advisory was also written by Yakov Shafranovich.
Timeline
201606-20: Android bug report filed with Google
2016-06-21: Android bug confirmed
2016-06-21: Bug also reported to Qualcomm and CERT.
2016-09-14: Coordination with Qualcomm on public disclosure
2016-09-15: Coordination with Google on public disclosure
2016-10-03: Android security bulletin released with fix
2016-10-04: Public disclosure
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