Pixel devices are lauded for their strong focus on security. This article peeks behind the scenes to explore how Pixel handles common vulnerabilities in cellular modems.
Smartphones have become indispensable in our lives, yet the intricate software powering them, especially the cellular baseband responsible for managing cellular communication like LTE, 4G, and 5G, is often overlooked. Given the tight performance constraints of baseband processors in most smartphones, enhancing security is challenging. Security experts have increasingly exploited this avenue and demonstrated the ability to compromise basebands used in popular smartphones.
The positive news is that Pixel has integrated security enhancements in our basebands for several years, with Pixel 9 boasting the most robustly secured baseband to date. This article delves into the importance of this endeavor, the specific security improvements, and the implications for our users.
Understanding the Cellular Baseband
The cellular baseband in a smartphone manages the device’s connectivity to cellular networks, involving the processing of external inputs that could come from untrusted sources. For example, attackers can use false base stations to inject fabricated or manipulated network packets, potentially exploiting certain protocols like IMS remotely via an IMS client.
Similar to any software, the firmware within the cellular baseband is vulnerable to bugs and errors. In the context of the baseband, these software vulnerabilities are concerning due to the heightened exposure of this component in the device’s attack surface. Evidence abounds of the exploitation of software bugs in modem basebands to achieve remote code execution, underscoring the critical risks posed by such vulnerabilities.
The Landscape of Baseband Security
Baseband security has become a focal point in security research, with demonstrations of software bug exploitation featuring prominently in various security conferences. These conferences also host training sessions dedicated to baseband firmware emulation, analysis, and exploitation techniques.
Recent reports by security researchers highlight that many basebands lack exploit mitigations considered best practices in software development, unlike mature software hardening techniques commonly found in the Android operating system. This gap poses risks that exploit vendors and cyber-espionage entities leverage to compromise individuals’ privacy without consent. The abuse of 0-day exploits in cellular basebands, leading to the deployment of malware like Predator in smartphones, and the listing of baseband exploits in exploit marketplaces point to a potential plethora of vulnerabilities that could grant attackers unauthorized access, enable arbitrary code execution, privilege escalation, or data extraction.
In light of these trends, Android and Pixel have proactively updated their Vulnerability Rewards Program to emphasize the identification and mitigation of exploitable bugs in connectivity firmware.
Constructing a Stronghold: Proactive Safeguards in the Pixel Modem
Responding to the escalating threat of baseband security attacks, Pixel has progressively integrated several proactive defenses over the years, with Pixel 9 smartphones showcasing the latest features:
- Bounds Sanitizer: This feature prevents buffer overflows by adding checks around memory accesses, ensuring that code does not access memory areas beyond what is designated.
- Integer Overflow Sanitizer: By adding checks around calculations, this feature prevents vulnerabilities arising from integer overflows that could lead to memory corruption.
- Stack Canaries: These act as safeguards to detect potential deviations in the flow of code execution, alerting the system to potential attacks.
- Control Flow Integrity (CFI): By constraining code execution to specific paths, CFI ensures that unauthorized execution paths trigger a restart rather than compromising the system.
- Auto-Initialize Stack Variables: To prevent vulnerabilities from uninitialized variables, Pixel automatically initializes stack variables to zero, eliminating risks associated with erroneous data leaks or exploitation.
During testing, we employ various bug detection tools like address sanitizer to identify software bugs and apply patches before shipping devices to our users.
The Pixel Edge: Consolidated Protections for Enhanced Security
While security enhancements are an ongoing challenge, the amalgamation of these safeguards significantly bolsters Pixel 9’s resilience against baseband attacks.
Pixel’s forward-thinking security approach reflects a steadfast commitment to safeguarding users across the software spectrum. Strengthening baseband security against remote attacks exemplifies Pixel’s continuous efforts to stay ahead in the security realm.
Acknowledgments to our colleagues who supported our endeavors in hardening cellular basebands: Dominik Maier, Shawn Yang, Sami Tolvanen, Pirama Arumuga Nainar, Stephen Hines, Kevin Deus, Xuan Xing, Eugene Rodionov, Stephan Somogyi, Wes Johnson, Suraj Harjani, Morgan Shen, Valery Wu, Clint Chen, Cheng-Yi He, Estefany Torres, Hungyen Weng, Jerry Hung, Sherif Hanna
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