CVE-2018-21054

Vulnerability

An integer underflow vulnerability exists in the eCryptFS implementation on Samsung mobile devices running Android M(6.0), N(7.x), and O(8.x), except for devices with specific chipsets (exynos9610/9820 on all platforms, MSM8909 SC77xx/9830 exynos3470/5420 on M(6.0), MSM8939 on N(7.0), MSM8996 SDM6xx/M6737T on N(7.1)). The flaw is triggered via a crafted input that causes an integer underflow, which subsequently results in a buffer overflow within the kernel's eCryptFS module. This vulnerability is identified by Samsung ID SVE-2017-11857 and was disclosed in September 2018 [no direct reference in provided texts, but cited in description].

Exploitation

An attacker requires local access to the device and the ability to interact with the eCryptFS filesystem. By crafting a specific sequence of filesystem operations (e.g., mounting or manipulating encrypted files), the attacker can induce an integer underflow. The underflow leads to a heap-based buffer overflow, corrupting kernel memory. No authentication beyond normal user access is needed; the attack does not require physical tampering, only the ability to execute code or commands on the device.

Impact

Successful exploitation allows an attacker to execute arbitrary code with kernel privileges. This leads to a full compromise of the device's confidentiality, integrity, and availability. The attacker can read sensitive data (e.g., encryption keys, user data), modify system files, and install persistent malware. The impact is severe, as it bypasses Android's security sandbox.

Mitigation

Samsung addressed this issue in security updates released after September 2018. The fix is included in the Samsung Mobile Security maintenance releases for affected devices. Users should apply the latest security patch level from their device's settings or carrier. No workaround is available for unpatched devices. The vulnerability is not listed in CISA's Known Exploited Vulnerabilities (KEV) catalog as of the publication date [1].