CVE-2017-18020

Vulnerability

On Samsung mobile devices with Lollipop (5.x), Marshmallow (6.x), and Nougat (7.x) software and Exynos chipsets, the S Boot bootloader omits a size check during a copy of ramfs data to memory. This missing boundary check in the bootloader's handling of the ramfs image allows attackers to trigger memory corruption. Affected versions include all Samsung devices using Exynos SoCs on those Android releases.

Exploitation

An attacker with physical or local access to the device can supply a specially crafted boot image (e.g., via fastboot or by replacing the kernel/ramfs partition). The bootloader does not validate the ramfs size before copying it into memory, enabling the attacker to overflow a buffer. No authentication or user interaction is required once the attacker has write access to the boot partition.

Impact

Successful exploitation allows arbitrary code execution within the bootloader context (S Boot), which runs before the kernel and operating system are loaded. This gives the attacker full control over the device at the highest privilege level, enabling persistent compromise that can bypass higher-level security controls like Android's verified boot.

Mitigation

Samsung has addressed this issue through its security update program; devices that have received the SVE-2017-10598 patch (incorporated into the monthly or quarterly maintenance release) are no longer vulnerable. Affected users should apply the latest firmware update from Samsung [1]. No workaround is available for unpatched devices.