Presented at
DEF CON 31 (2023),
Aug. 11, 2023, noon
(45 minutes)
Prepaid Android smartphones present an attractive option since they can be used and discarded at will without significant financial cost. The reasons for their use are manifold, although some people may use them to dissemble their true identity. Prepaid smartphones offer value, but there may be an additional "cost" for their cheap price. We present an examination of the local attack surface of 21 prepaid Android smartphones sold by American carriers (and 11 unlocked smartphones). While examining these devices, we discovered instances of arbitrary command execution in the context of a "system" user app, arbitrary AT command execution, arbitrary file write in the context of the Android System (i.e., "system_server"), arbitrary file read/write in the context of a "system" user app, programmatic factory reset, leakage of GPS coordinates to a loopback port, numerous exposures of non-resettable device identifiers to system properties, and more.
The only user interaction that our threat model assumes is that the user installs and runs a third-party app that has no permissions or only a single "normal" level permission that is automatically granted to the third-party app upon installation. The installed third-party app can leverage flaws in pre-loaded software to escalate privileges to indirectly perform actions or obtain data while lacking the necessary privileges to do so directly. Due to a wide range of local interfaces with missing access control checks and inadequate input validation, a third-party app’s behavior is not truly circumscribed by the permissions that it requests. Due to the common inclusion of pre-loaded software from Android vendors, chipset manufacturers, carriers, and vendor partners, exploit code can have significant breadth. The inter-app communication used to exploit these vulnerabilities may be difficult to classify as inherently malicious in general since it uses the standard communication channels employed by non-malicious apps.
We pick up again where we left off from our DEF CON 26 talk … raiding the prepaid Android smartphone aisles at Walmart. We provide another snapshot on the state of security for Android carrier devices. In this talk, we examine 21 different prepaid Android smartphones being sold by the major American carriers, and we also cover 11 unlocked Android devices, which are primarily ZTE smartphones. We identified vulnerabilities in multiple layers of the Android software stack. For each discovered vulnerability, we step through the attack requirements, access vector, and attack workflow in order to help developers and bug hunters identify common software flaws going forward.
REFERENCES:
https://support.zte.com.cn/support/news/LoopholeInfoDetail.aspx?newsId=1030664
https://www.bleepingcomputer.com/news/security/oneplus-phones-come-preinstalled-with-a-factory-app-that-can-root-devices/
https://source.android.com/docs/security/features/selinux#background
https://en.wikipedia.org/wiki/Confused_deputy_problem
https://github.com/thanuj10/Nokia-Debloater
https://developer.android.com/training/articles/user-data-ids#best-practices-android-identifiers
https://android.googlesource.com/platform/hardware/ril/+/master/include/telephony/ril.h
https://github.com/lbule/android_hardware_mediatek
https://security.tecno.com/SRC/blogdetail/99?lang=en_US
https://extensionpublications.unl.edu/assets/pdf/ec157.pdf
https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/service/persistentdata/PersistentDataBlockManager.java#143
https://github.com/ptoomey3/evilarc/blob/master/evilarc.py
https://android.googlesource.com/platform/frameworks/base/+/master/packages/SystemUI/
https://android.googlesource.com/platform/packages/apps/Settings/+/refs/heads/master
Presenters:
-
Angelos Stavrou
- Founder and Chief Scientist at Quokka
Dr. Angelos Stavrou is Founder and Chief Scientist of Quokka (formerly Kryptowire), a Virginia based Mobile Security company. He is also a Professor at the Bradley Department of Electrical & Computer Engineering at Virginia Tech. Dr. Stavrou has served as principal investigator on research awards from NSF, DARPA, IARPA, DHS, AFOSR, ARO, ONR. He is an active member of NIST's Mobile Security team and has written more than 130 peer-reviewed conference and journal articles. Dr. Stavrou received his M.Sc. in Electrical Engineering, M.Phil. and Ph.D. (with distinction) in Computer Science all from Columbia University. He also holds an M.Sc. in theoretical Computer Science from the University of Athens and a B.Sc. in Physics with distinction from the University of Patras, Greece. Stavrou is an Associate Editor of IEEE Transactions on Computers, IEEE Security & Privacy, and IEEE Internet Computing magazines and a previous co-chair of the IEEE Blockchain initiative. Over the past few years, Dr. Stavrou's research has focused on two aspects of security: Systems' Security and Reliability. Dr. Stavrou is a member of USENIX, and a senior member of ACM and IEEE.
-
Mohamed Elsabagh
- Senior Director, R&D at Quokka
Dr. Mohamed Elsabagh leads the research and development efforts at Quokka (formerly Kryptowire). He specializes in automated static/dynamic binary security analysis and reverse engineering for Android, ARM, and x86 platforms. He has created several tools that helped detect and prevent hundreds of zero-day vulnerabilities in the wild. Mohamed holds a PhD in CS during which he developed automated binary hardening techniques for COTS systems.
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Ryan Johnson
- Senior Director, R&D at Quokka
Dr. Ryan Johnson is a Senior Director, R&D at Quokka (formerly Kryptowire). His research interests are static and dynamic analysis of Android apps and reverse engineering. He is a co-founder of Quokka and has presented at DEF CON, Black Hat (USA, Asia, & MEA), IT-Defense, and @Hack. His research in Android security has been assigned dozens of CVEs and is responsible for discovering the Adups spyware that affected millions of Android smartphones.
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