CVE-2017-18020 in Samsung
Summary
by MITRE
On Samsung mobile devices with L(5.x), M(6.x), and N(7.x) software and Exynos chipsets, attackers can execute arbitrary code in the bootloader because S Boot omits a size check during a copy of ramfs data to memory. The Samsung ID is SVE-2017-10598.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 12/19/2019
This vulnerability exists in Samsung mobile devices running android versions lollipop 5.x marshmallow 6.x and nougat 7.x that utilize exynos chipsets. The flaw resides within the s boot component of the bootloader which is responsible for initializing the device and loading the operating system. The vulnerability stems from a critical omission in the s boot implementation where it fails to perform proper size validation when copying ramfs data to memory. Ramfs or ram filesystem is a temporary filesystem that resides in memory and is commonly used during the boot process to provide access to essential files before the full filesystem is mounted. The absence of size checking creates a condition where an attacker can potentially overflow the allocated memory buffer during the copy operation.
The technical exploitation of this vulnerability allows attackers to execute arbitrary code at the bootloader level which represents one of the most privileged execution contexts on a mobile device. When the bootloader copies ramfs data without validating the size of the incoming data, an attacker can craft malicious input that exceeds the allocated buffer space. This buffer overflow condition enables the execution of arbitrary code with the highest possible privileges since the bootloader operates before the operating system kernel and security mechanisms are initialized. The attack vector typically involves manipulating the ramfs data that is passed to the bootloader during the device initialization process, potentially through compromised update mechanisms or specially crafted boot images.
The operational impact of this vulnerability is severe as it provides attackers with root access to the device at the earliest possible stage of the boot process. This means that any code executed through this vulnerability can bypass all subsequent security measures including encryption, secure boot, and application level protections. The attack can potentially result in complete device compromise, data exfiltration, and persistent backdoor access. Since this affects the bootloader level, it can be exploited even if the device is running the latest security patches for the operating system, as the vulnerability exists at a lower level in the device firmware. The vulnerability affects a significant number of samsung devices since lollipop marshmallow and nougat were widely deployed across various smartphone models.
The vulnerability aligns with common weakness enumeration cwe-129 which describes improper validation of the length of input data. This weakness specifically addresses situations where programs fail to validate the size of input data before processing it, leading to buffer overflows and arbitrary code execution. From an attack perspective this vulnerability maps to multiple techniques within the attack tactics and techniques framework including privilege escalation through bootkit or rootkit attacks and execution of malicious code at the system level. The attack can be categorized under the initial access phase of the attack lifecycle where the attacker gains entry through the bootloader and maintains persistence. Samsung addressed this vulnerability through firmware updates and improved validation mechanisms in subsequent bootloader versions, but devices that remain unpatched continue to be at risk. The vulnerability demonstrates the critical importance of proper input validation even in low-level firmware components and highlights the need for robust security practices in the bootloader and early boot stages of mobile devices.