Introduction:
Modern mobile devices share similarities with desktop computers, yet possess distinct features that set them apart. Alongside cellular capabilities and multiple communication channels, smartphones and tablets integrate sensors, cryptographic processors, HD cameras, touch screens, and various wired and wireless interfaces.
The key architectural distinction in smartphones and tablets with cellular capabilities lies between the general-purpose mobile operating system (OS) and the hardware and firmware responsible for accessing cellular networks, commonly referred to as the baseband or telephony subsystem. This subsystem runs on a real-time operating system (RTOS) and handles essential communication tasks, such as managing cellular signals. Typically housed on the same System on a Chip (SoC) as the application processor, or as a separate chip, the baseband is crucial to ensuring that mobile devices can reliably connect to cellular networks.
While the baseband plays a foundational role in mobile communication, it also represents a significant attack vector. The baseband processor often operates with elevated privileges and parses untrusted inputs—such as signals from cellular networks—that can be remotely delivered to the device. Consequently, baseband vulnerabilities can serve as entry points for more sophisticated cyberattacks. Exploiting such vulnerabilities can allow attackers to infiltrate deeper layers of the device, potentially gaining control over the entire system.
Historically, the baseband has been an under-protected component compared to other parts of mobile devices. Security research has consistently exposed a lack of modern exploit mitigations in baseband firmware, making it an attractive target for attackers. Remote Code Execution (RCE) vulnerabilities in the baseband can allow attackers to execute arbitrary code, leading to a variety of consequences, from stealing sensitive data to intercepting calls or tracking the user’s location.
Given the growing attention on this attack surface, baseband exploitation has become a recurring topic at security conferences, and baseband bugs are even traded in third-party exploit marketplaces. The Android security team has responded to this threat by prioritizing the hardening of baseband firmware. For example, Google has adopted sanitizers such as Integer Overflow Sanitizer (IntSan) and BoundsSanitizer (BoundSan) to detect and mitigate common vulnerabilities like integer overflows and out-of-bounds access. These sanitizers improve the code’s stability and security, providing runtime checks that can prevent potential vulnerabilities from being exploited.
Despite these efforts, the challenge remains substantial. As cellular technology continues to evolve with the proliferation of 5G and beyond, the complexity of baseband firmware increases, introducing new potential vulnerabilities. Researchers warn that the baseband’s security has not kept pace with advancements in network functionality, leaving gaps that sophisticated attackers could exploit.
Understanding and addressing baseband vulnerabilities is essential because they serve as a critical gateway into mobile devices. Once the baseband is compromised, attackers can bypass other security layers, gaining access to sensitive user data, intercepting communications, or disabling critical device functions. Therefore, securing the baseband is not just about protecting cellular connectivity—it’s about safeguarding the entire mobile ecosystem.
Keen Security Lab Baseband Vulnerabilities – Case Study:
In a significant cybersecurity discovery in 2021, Keen Security Lab, a renowned security research group, unearthed a severe vulnerability within the baseband chips of various 5G smartphones. This vulnerability, which can potentially impact multiple Qualcomm chipset families, including Snapdragon Auto, Snapdragon Compute, Snapdragon Connectivity, Snapdragon Industrial IoT, and Snapdragon Mobile, stemmed from a lack of input validation in the modem firmware, the component responsible for managing cellular communication. Attackers could exploit this weakness by crafting malicious data packets that could be interpreted and executed by the baseband chip, leading to a wide range of detrimental consequences.
The vulnerability stemmed from a lack of input validation in the modem firmware, which is responsible for managing cellular communication. Attackers could exploit this weakness by crafting malicious data packets that could be interpreted and executed by the baseband chip. This could lead to a wide range of attacks, including:
- Remote code execution: Attackers could gain full control of the device, allowing them to install malware, steal sensitive data, or disrupt cellular connectivity.
- Call interception: Attackers could intercept calls, eavesdropping on conversations or injecting malicious audio content.
- Location tracking: Attackers could track a device’s location, potentially monitoring users’ movements.
The vulnerability affected several baseband chips from major manufacturers, including Qualcomm, MediaTek, Samsung, and Intel.
This vulnerability is part of a multi-stage attack, with the first stage being the most critical, involving the interruption of the communication channel via a “man-in-the-middle” or “replay” attack. What is particularly alarming is that, despite the uncertainty surrounding whether the vulnerability has been adequately patched, security researchers have concluded that:
The security of baseband chips has not kept pace with the advancements in network functionalities, significantly trailing behind the security measures implemented on the access point (AP) side.
Some baseband chips lack even the most basic security features, leaving them vulnerable to a wide range of attacks.
Some related critical Common Vulnerabilities and Exposures (CVEs) include:
- CVE-2021-35082: This CVE is for a critical vulnerability in the Qualcomm Snapdragon X55 modem firmware that could allow attackers to remotely execute code on the baseband chip. The vulnerability is caused by a lack of input validation in the modem firmware, which could allow attackers to craft malicious data that could be executed by the baseband chip.
- CVE-2021-35090: This CVE is for a critical vulnerability in the Qualcomm Snapdragon X60 modem firmware that could allow attackers to remotely execute code on the baseband chip. The vulnerability is caused by a lack of input validation in the modem firmware, which could allow attackers to craft malicious data that could be executed by the baseband chip.
- CVE-2021-35072: This CVE is for a high vulnerability in the Qualcomm Snapdragon X55 modem firmware that could allow attackers to remotely execute code on the baseband chip. The vulnerability is caused by a lack of input validation in the modem firmware, which could allow attackers to craft malicious data that could be executed by the baseband chip.
Conclusion:
As the high-level operating system becomes increasingly hardened and difficult for attackers to exploit, attention is shifting toward lower-level components like the baseband. These components, often less protected yet critical to device functionality, represent attractive targets for sophisticated cyberattacks. Strengthening the security of baseband processors through modern toolchains, exploit mitigation technologies like sanitizers, and transitioning to memory-safe languages such as Rust will help raise the bar for attackers. However, with evolving threats and growing complexity in cellular communication, continuous vigilance and innovation are essential to safeguard mobile devices from baseband-related vulnerabilities.
Intellectra is actively developing innovative solutions designed to identify and mitigate this type of attack at its earliest stage.
This undertaking presents a formidable challenge, as effectively detecting these attacks without compromising cellular service or generating excessive false positives is extremely demanding.
References:
- Marco Grassi, Xingyu Chen, “Over The Air Baseband Exploit: Gaining Remote
Code Execution on 5G Smartphones”, Keen Security Lab of Tencent, 2021 - Mitre: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-35082
- NIST, National Vulnerability Database
- Google Security Blog, Hardening Cellular Basebands in Android, December 2023
