CVE-2021-39719 in Android
Summary
by MITRE • 03/16/2022
In lwis_top_register_io of lwis_device_top.c, there is a possible out of bounds write due to an integer overflow. This could lead to local escalation of privilege with System execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-205995178References: N/A
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Analysis
by VulDB Data Team • 03/19/2022
The vulnerability identified as CVE-2021-39719 resides within the lwis_device_top.c source file of the Android kernel, specifically in the lwis_top_register_io function. This flaw represents a critical security weakness that stems from improper input validation and arithmetic handling within the kernel's device management subsystem. The vulnerability manifests as a potential out of bounds write condition that arises from an integer overflow during the processing of I/O register operations.
The technical root cause of this vulnerability lies in the improper handling of integer values during register I/O operations within the lwis device driver. When the lwis_top_register_io function processes incoming register access requests, it fails to properly validate the size parameters or perform adequate bounds checking before writing to memory locations. This integer overflow condition occurs when the calculation of buffer offsets or memory boundaries exceeds the maximum representable value for the integer type being used, leading to unexpected memory access patterns that can overwrite adjacent memory locations.
From an operational perspective, this vulnerability presents a significant risk for local privilege escalation attacks within the Android kernel environment. The flaw requires system execution privileges for exploitation but does not necessitate user interaction, making it particularly dangerous as it can be leveraged by malicious processes already running with system-level permissions. An attacker who can manipulate the I/O register operations could potentially overwrite critical kernel data structures or function pointers, leading to arbitrary code execution with full system privileges. This represents a direct pathway to privilege escalation that aligns with the ATT&CK technique T1068 for local privilege escalation and T1543 for privilege escalation through kernel exploits.
The impact of this vulnerability extends beyond simple memory corruption, as it can potentially compromise the entire kernel integrity and system stability. The integer overflow condition could be exploited to overwrite kernel memory regions that control critical system operations, potentially allowing an attacker to modify kernel code or data structures that govern system behavior. This type of vulnerability falls under CWE-190, Integer Overflow or Wraparound, which specifically addresses the improper handling of integer arithmetic that can lead to unexpected behavior and security exploits.
Mitigation strategies for CVE-2021-39719 should focus on implementing proper input validation and bounds checking within the lwis device driver's register I/O handling functions. The most effective approach involves adding comprehensive parameter validation to ensure that all register access operations remain within valid memory boundaries and that integer calculations do not overflow. Additionally, the implementation of proper signed integer overflow detection mechanisms and bounds checking routines should be enforced throughout the lwis device driver codebase. System administrators should ensure that affected Android kernel versions are updated with patches that address this specific integer overflow condition and that proper kernel hardening measures are implemented to prevent similar vulnerabilities from occurring in other kernel subsystems. The vulnerability demonstrates the critical importance of robust input validation in kernel space operations and aligns with the principle of least privilege enforcement that should be applied to all kernel-level drivers and subsystems.