CVE-2018-21089 in Samsung
Summary
by MITRE
An issue was discovered on Samsung mobile devices with N(7.x) (MT6755/MT6757 Mediatek models) software. Bootloader has an integer overflow that leads to arbitrary code execution via the download offset control. The Samsung ID is SVE-2017-10732 (January 2018).
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Analysis
by VulDB Data Team • 10/09/2020
The vulnerability identified as CVE-2018-21089 represents a critical security flaw affecting Samsung mobile devices running Android 7.x operating systems with MediaTek MT6755 or MT6757 chipsets. This issue resides within the bootloader component of these devices, which serves as the foundational software layer that initializes the operating system and establishes the initial execution environment. The bootloader's role in the device security architecture makes it a prime target for attackers seeking to establish persistent control over the device. The vulnerability manifests as an integer overflow condition that occurs during the processing of download offset controls, which are mechanisms used during firmware flashing operations.
The technical flaw stems from improper input validation within the bootloader's handling of offset parameters during firmware download operations. When an attacker crafts malicious firmware images with carefully manipulated offset values, the integer overflow condition causes the bootloader to misinterpret these values, potentially leading to memory corruption. This memory corruption can be exploited to redirect code execution flow, allowing attackers to load and execute arbitrary code within the bootloader context. The vulnerability's exploitation requires the attacker to have access to the device's download mode, which is typically accessible through specific hardware combinations or USB debugging interfaces. The integer overflow specifically affects the calculation of memory addresses or buffer boundaries, where the overflowed value can be used to overwrite critical system structures or jump to attacker-controlled code locations. This type of vulnerability falls under the CWE-190 category of Integer Overflow or Wraparound, which is classified as a fundamental software flaw that can lead to severe security consequences.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with the capability to bypass critical security mechanisms within the device's boot process. Since the exploitation occurs at the bootloader level, it can potentially circumvent all subsequent security measures including verified boot, encryption, and secure boot features. This means that an attacker who successfully exploits this vulnerability could install malicious firmware that persists across device reboots and remains operational even after software updates. The attack surface is particularly concerning for devices that support USB debugging or have download mode enabled, as these interfaces can be accessed through physical interaction or specific attack vectors. The vulnerability's timing, occurring in 2018, indicates that it affected a significant number of Samsung devices that were still in use, potentially leaving millions of devices vulnerable to exploitation by threat actors who discovered and weaponized this flaw.
Mitigation strategies for this vulnerability require a multi-layered approach that addresses both immediate protection and long-term security improvements. Device manufacturers should prioritize firmware updates that correct the integer overflow condition within the bootloader, ensuring that proper input validation is implemented to prevent malicious offset values from causing memory corruption. System administrators and security teams should disable unnecessary USB debugging interfaces and download mode access on devices that do not require these features for legitimate operations. Network security controls should monitor for suspicious firmware update activities or attempts to establish unauthorized connections to device download modes. The vulnerability's characteristics align with ATT&CK technique T1014, which involves rootkit or bootkit techniques, and T1027, which covers obfuscated files or information, as attackers may attempt to hide malicious payloads within legitimate firmware updates. Organizations should implement robust device management policies that enforce secure boot requirements and regularly audit device configurations to prevent unauthorized access to download interfaces. Additionally, security researchers and vendors should collaborate to ensure that such vulnerabilities are properly disclosed and patched in a timely manner to prevent exploitation by malicious actors who may have already discovered and weaponized these flaws.