CVE-2018-20788 in Redmi 6pro
Summary
by MITRE
drivers/leds/leds-aw2023.c in the led driver for custom Linux kernels on the Xiaomi Redmi 6pro daisy-o-oss phone has several integer overflows because of a left-shifting operation when the right-hand operand can be equal to or greater than the integer length. This can be exploited by a crafted application for denial of service.
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Analysis
by VulDB Data Team • 07/19/2023
The vulnerability identified as CVE-2018-20788 resides within the led driver implementation for the Xiaomi Redmi 6pro device, specifically in the drivers/leds/leds-aw2023.c file. This issue manifests as integer overflow conditions that occur during left-shift operations when the shift amount parameter equals or exceeds the bit width of the integer type being manipulated. The affected device operates on a custom Linux kernel configuration that is specific to the daisy-o-oss phone variant, indicating this vulnerability is not present in standard kernel distributions but rather in proprietary or modified kernel implementations used by Xiaomi for their mobile devices.
The technical flaw stems from improper input validation and arithmetic overflow handling within the LED driver's control logic. When a malicious application provides crafted parameters to the LED subsystem, the driver performs left-shift operations with potentially dangerous shift values that exceed the integer's bit capacity. This leads to undefined behavior where the shifted value wraps around or becomes zero, creating conditions that can cause the kernel to crash or become unresponsive. The vulnerability specifically relates to CWE-191 Integer Underflow/Overflow, which is classified as a critical weakness in software security that can lead to system instability and denial of service conditions. The implementation lacks proper bounds checking before performing bitwise operations, allowing attackers to manipulate the shift operands to create overflow scenarios.
The operational impact of this vulnerability is significant for the targeted device, as it enables a local attacker with application-level privileges to cause a denial of service condition that affects the device's LED functionality and potentially the overall system stability. Since the vulnerability exists in the kernel driver level, any application with sufficient privileges can exploit it to crash the LED subsystem or cause system-wide instability. This represents a serious security concern for mobile devices where LED functionality is often used for notifications, status indicators, and user feedback mechanisms. The attack vector requires only local application execution, making it particularly dangerous as it can be exploited through malicious apps installed on the device or through compromised applications that gain the necessary permissions to interact with the LED subsystem.
Mitigation strategies for this vulnerability should focus on kernel-level patches that implement proper bounds checking before left-shift operations and validate input parameters to prevent overflow conditions. The fix should include explicit range validation for shift operands to ensure they remain within acceptable limits relative to the integer type being used. Additionally, system administrators and device manufacturers should implement proper input sanitization and parameter validation in all kernel drivers that perform bitwise operations. This vulnerability demonstrates the importance of following secure coding practices and adhering to established security guidelines such as those outlined in the CERT Secure Coding Standards, which specifically address integer overflow conditions and recommend defensive programming techniques. The ATT&CK framework categorizes this as a privilege escalation technique through kernel vulnerabilities, as it allows local applications to gain control over system resources and cause denial of service conditions that can be leveraged for further exploitation. Device manufacturers should also consider implementing runtime monitoring and anomaly detection for kernel-level operations to identify and prevent exploitation attempts before they can cause system instability.