Google Android - 'gpsOneXtra' Data Files Denial of Service

Original at:

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