CVE-2024-42135 in Linux
Summary
by MITRE • 07/30/2024
In the Linux kernel, the following vulnerability has been resolved:
vhost_task: Handle SIGKILL by flushing work and exiting
Instead of lingering until the device is closed, this has us handle SIGKILL by:
1. marking the worker as killed so we no longer try to use it with new virtqueues and new flush operations. 2. setting the virtqueue to worker mapping so no new works are queued. 3. running all the exiting works.
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Analysis
by VulDB Data Team • 07/19/2025
The vulnerability identified as CVE-2024-42135 resides within the Linux kernel's vhost subsystem, specifically affecting the vhost_task implementation that manages virtual host worker threads. This issue represents a critical race condition and improper signal handling mechanism that could lead to system instability and potential denial of service conditions. The vhost subsystem is integral to virtualization environments, particularly when utilizing virtio devices for communication between host and guest operating systems. The flaw manifests when the kernel's vhost_task component fails to properly handle SIGKILL signals, which are typically used to forcefully terminate processes. This improper handling creates a scenario where worker threads may remain in an inconsistent state, potentially leading to resource leaks, memory corruption, or system crashes when attempting to manage virtual queue operations.
The technical flaw stems from the absence of proper cleanup procedures when SIGKILL signals are received by vhost worker threads. Under normal circumstances, when a process receives SIGKILL, the kernel should immediately terminate the process and perform necessary cleanup operations. However, in this case, the vhost_task implementation fails to properly flush pending work items and clean up worker state before exiting. This creates a dangerous condition where worker threads may continue to reference invalid memory locations or attempt to process work items that should have been discarded. The vulnerability specifically affects the virtio subsystem's ability to manage worker threads efficiently, as the implementation does not adequately address the transition from active work processing to graceful termination. This issue falls under CWE-404, which deals with improper resource cleanup, and represents a failure to properly handle process termination signals in multi-threaded environments. The flaw is particularly concerning in virtualized environments where multiple vhost workers may be simultaneously managing different virtio queues.
The operational impact of CVE-2024-42135 extends beyond simple process termination issues, potentially affecting entire virtualization platforms and cloud infrastructure deployments. When a SIGKILL signal is sent to a vhost worker thread, the system may experience resource leaks where memory allocated for work items remains unreleased, leading to gradual memory exhaustion over time. Additionally, the improper handling can cause work items to be queued to invalid worker mappings, resulting in system crashes or kernel panics when these invalid references are eventually processed. This vulnerability directly impacts the ATT&CK technique T1490, which involves creating or manipulating system resources to cause denial of service conditions. The flaw can be exploited by malicious actors to perform resource exhaustion attacks against virtualization hosts, potentially leading to service disruption for multiple virtual machines running on the same host. In containerized environments utilizing virtio devices, this vulnerability could allow attackers to compromise the stability of container orchestration systems, as the vhost subsystem is frequently used for network and storage virtualization in such deployments.
Mitigation strategies for CVE-2024-42135 should focus on immediate kernel updates and system hardening measures. Organizations should prioritize applying the latest kernel patches that address this specific vulnerability, as the fix involves proper handling of SIGKILL signals through explicit worker state marking and work flushing operations. The recommended approach includes implementing proper signal handling that marks workers as killed, prevents new work from being queued to invalid mappings, and ensures all pending work items are processed before thread termination. System administrators should also monitor for unusual process termination patterns in virtualization environments and implement resource limits to prevent potential resource exhaustion attacks. Additional defensive measures include configuring proper logging of vhost worker activities and implementing intrusion detection systems that can identify abnormal signal handling patterns. The fix aligns with security best practices outlined in the Linux kernel security documentation, particularly regarding proper signal handling in multi-threaded kernel subsystems. Organizations should also consider implementing virtualization-specific security controls such as hypervisor hardening, container isolation measures, and regular security assessments of virtualized environments to prevent exploitation of similar vulnerabilities in related subsystems.