CVE-2019-3819 in Linux
Summary
by MITRE
A flaw was found in the Linux kernel in the function hid_debug_events_read() in drivers/hid/hid-debug.c file which may enter an infinite loop with certain parameters passed from a userspace. A local privileged user ("root") can cause a system lock up and a denial of service. Versions from v4.18 and newer are vulnerable.
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Analysis
by VulDB Data Team • 02/11/2025
The vulnerability identified as CVE-2019-3819 represents a critical flaw in the Linux kernel's Human Interface Device (HID) subsystem that can lead to system instability and denial of service conditions. This issue resides within the hid_debug_events_read() function located in the drivers/hid/hid-debug.c file, which is part of the kernel's HID driver implementation. The flaw specifically manifests when certain parameters are passed from userspace to this kernel function, creating a condition that can result in an infinite loop execution. The vulnerability affects Linux kernel versions from v4.18 and newer, indicating that a substantial portion of modern kernel releases remain susceptible to this issue.
The technical nature of this vulnerability stems from inadequate input validation and parameter handling within the kernel's HID debugging interface. When a local privileged user with root access executes specific sequences of operations that trigger the hid_debug_events_read() function, the kernel enters a pathological state where the function fails to properly terminate execution. This infinite loop condition occurs because the function does not adequately check for boundary conditions or parameter constraints that would normally cause the loop to exit. The flaw essentially creates a situation where kernel execution becomes trapped in a continuous loop, consuming system resources and preventing normal kernel operations from proceeding. From a cybersecurity perspective, this represents a classic example of a denial of service vulnerability that can be exploited by authenticated users with elevated privileges.
The operational impact of CVE-2019-3819 is severe and directly affects system availability and stability. A local privileged user with root access can deliberately trigger this vulnerability to cause a complete system lockup, effectively rendering the affected system unusable until a manual reboot occurs. This type of denial of service attack is particularly concerning because it requires only local access with root privileges, making it accessible to users who already have significant system control. The vulnerability essentially allows an attacker to compromise system availability without requiring external network access or complex exploitation techniques. The infinite loop condition can consume all available CPU cycles for the affected kernel thread, causing cascading effects that may impact other system processes and services running on the compromised machine. This vulnerability aligns with ATT&CK technique T1499.004, which involves network denial of service, although in this case the impact occurs at the kernel level rather than network infrastructure.
Mitigation strategies for CVE-2019-3819 focus primarily on kernel updates and system hardening measures. The most effective solution involves upgrading to a patched Linux kernel version that addresses the specific flaw in the hid_debug_events_read() function. Kernel maintainers released fixes that properly validate input parameters and implement appropriate loop termination conditions to prevent the infinite loop scenario. System administrators should also consider disabling the HID debugging interface when it is not actively needed, as this can prevent exploitation of the vulnerability through userspace interfaces. Additionally, implementing proper access controls and privilege management can limit the potential impact of this vulnerability by restricting root access to only necessary users and processes. The vulnerability demonstrates the importance of proper kernel code review and input validation, particularly in debugging interfaces that may be exposed to untrusted userspace processes. Organizations should also consider implementing monitoring solutions that can detect anomalous CPU usage patterns that might indicate exploitation attempts, providing early warning capabilities for such denial of service conditions.
This vulnerability serves as a reminder of the critical importance of kernel security and the potential for seemingly benign debugging interfaces to become attack vectors. The flaw exemplifies CWE-691, which covers inadequate input validation in kernel interfaces, and highlights the need for comprehensive security testing of kernel subsystems. The issue also demonstrates how privilege escalation within a system can be leveraged to create denial of service conditions that can impact overall system availability and user experience. Organizations should maintain up-to-date kernel security patches and implement robust monitoring to detect potential exploitation attempts, particularly in environments where root access is widely distributed or where system stability is critical for business operations.