CVE-2020-0433 in Android
Summary
by MITRE
In blk_mq_queue_tag_busy_iter of blk-mq-tag.c, there is a possible use after free due to improper locking. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-151939299
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Analysis
by VulDB Data Team • 09/18/2020
The vulnerability identified as CVE-2020-0433 resides within the Android kernel's block I/O subsystem, specifically in the blk_mq_queue_tag_busy_iter function located in blk-mq-tag.c. This flaw represents a classic use-after-free vulnerability that arises from inadequate locking mechanisms during concurrent access to shared data structures. The issue manifests when multiple threads attempt to access and modify tag queue data structures without proper synchronization, creating a window where freed memory can be accessed by subsequent operations.
The technical root cause of this vulnerability stems from improper locking protocols within the block multi-queue tagging system. When the blk_mq_queue_tag_busy_iter function processes tag iterations, it fails to maintain consistent lock ordering or acquire appropriate locks before accessing shared tag structures. This race condition allows an attacker to potentially free memory while another thread still holds a reference to it, resulting in undefined behavior that can be exploited for privilege escalation. The vulnerability operates at the kernel level where the security boundaries between user and kernel space are breached, making it particularly dangerous for local attackers who can leverage this flaw to gain elevated privileges.
From an operational perspective, this vulnerability presents a significant risk to Android devices as it requires no user interaction for exploitation and can be leveraged for local privilege escalation. The attack vector is particularly concerning because it operates entirely within the kernel space where the attacker already has access to the system. The exploitation process involves manipulating concurrent access patterns to trigger the race condition, potentially allowing an attacker to execute arbitrary code with kernel privileges. This capability directly violates the principle of least privilege and undermines the fundamental security model of the Android operating system, as it enables local users to escalate their privileges without requiring additional malicious payloads or user interaction.
The impact of this vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software systems. This classification emphasizes the dangerous nature of accessing memory after it has been freed, creating opportunities for memory corruption and arbitrary code execution. The vulnerability also relates to ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation" and demonstrates how kernel-level flaws can be exploited to gain elevated system privileges. Security professionals should note that this vulnerability is particularly insidious because it operates below the level of traditional user-space protections, making detection and prevention more challenging.
Mitigation strategies for CVE-2020-0433 should focus on implementing proper locking mechanisms within the blk_mq_queue_tag_busy_iter function and ensuring that all shared data structures are accessed with appropriate synchronization primitives. Android security teams should prioritize patching affected kernel versions and implementing additional runtime checks to prevent the exploitation of race conditions. System administrators should monitor for any signs of privilege escalation attempts and ensure that kernel updates are applied promptly. The vulnerability underscores the importance of rigorous code review processes for kernel subsystems and highlights the need for comprehensive testing of concurrent access patterns to prevent similar race condition vulnerabilities from emerging in other parts of the system.