CVE-2019-1998 in Android
Summary
by MITRE
In event_handler of keymaster_app.c, there is possible resource exhaustion due to a table being lost on reboot. This could lead to local denial of service that is not fixed by a factory reset, with no additional execution privileges needed. User interaction is not needed for exploitation. Product: Android. Versions: Android-9. Android ID: A-116055338.
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Analysis
by VulDB Data Team • 07/26/2023
The vulnerability described in CVE-2019-1998 represents a critical resource exhaustion issue within the Android keymaster implementation that affects Android 9.0 systems. This flaw exists in the event_handler function of keymaster_app.c, which is part of the Android Keystore system responsible for managing cryptographic keys and operations. The vulnerability stems from a specific memory management issue where a table structure becomes inaccessible or lost during system reboot processes, creating a persistent resource leak that accumulates over time.
The technical nature of this vulnerability is rooted in improper resource cleanup during system restart sequences. When the Android system reboots, the keymaster application fails to properly maintain or reclaim certain table structures that are essential for key management operations. This results in a gradual depletion of available system resources, particularly memory and potentially file descriptors or other kernel objects that the keymaster service relies upon. The issue manifests as a resource exhaustion condition that can ultimately lead to a complete denial of service for the keymaster service, rendering cryptographic operations unavailable to applications that depend on secure key storage and management.
From an operational perspective, this vulnerability presents a particularly concerning threat because it persists beyond standard recovery mechanisms such as factory resets. The fact that no additional execution privileges are required for exploitation means that any local user or application with basic system access can trigger this condition. The lack of user interaction requirements makes this vulnerability especially dangerous as it can be exploited silently in the background without any visible warning signs to users or administrators. This characteristic places the vulnerability in the ATT&CK matrix category of privilege escalation and denial of service, specifically under the technique of resource exhaustion attacks.
The impact of this vulnerability extends beyond simple service disruption, as it affects the fundamental security infrastructure of Android devices. The keymaster service is critical for secure key storage, encryption operations, and overall device security. When this service becomes unavailable due to resource exhaustion, applications that depend on secure cryptographic operations may fail, potentially leading to data corruption, unauthorized access to encrypted data, or complete loss of secure communication capabilities. This vulnerability also represents a failure in the Android security model's resource management, as it demonstrates how improper cleanup during system restart can create persistent security weaknesses that are difficult to detect and remediate.
Mitigation strategies for this vulnerability should focus on implementing proper resource cleanup mechanisms within the keymaster application during system reboot events. System administrators and device manufacturers should ensure that all table structures and resource allocations are properly reclaimed during shutdown and restart processes. The fix should involve code modifications to keymaster_app.c that guarantee proper deallocation of memory structures even when the system undergoes unexpected restarts. Additionally, implementing monitoring and alerting mechanisms that can detect resource exhaustion conditions in the keymaster service would help identify when this vulnerability is being exploited or when the system is approaching critical resource depletion levels. Organizations should also consider implementing regular system health checks and automated recovery procedures that can detect and remediate resource exhaustion conditions before they lead to complete service failure, aligning with industry best practices for maintaining system integrity and availability.