CVE-2026-98112 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix listener task lifetime on netdev events
The listener thread exits when its listening socket is shutdown. The netdevice notifier shuts down the socket before calling kthread_stop(), so the task_struct can be freed before kthread_stop() gets its reference.
Create the listener in a stopped state and hold an extra task_struct reference until kthread_stop_put() completes. Also stop and release listeners before freeing their interface records during TCP teardown.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified within the Linux kernel's ksmbd subsystem represents a critical race condition involving thread lifecycle management and memory safety, specifically triggered by network device state changes. The core technical flaw stems from an improper ordering of operations when handling netdevice events. In this scenario, the listener thread is designed to exit upon receiving a shutdown signal for its listening socket. However, the implementation incorrectly initiates the socket shutdown before invoking kthread_stop(). This sequence creates a window where the kernel's network subsystem may free resources associated with the interface while the task structure representing the listener thread is still in use or being accessed. Consequently, this leads to a situation where the task_struct can be freed prematurely, prior to kthread_stop() successfully acquiring its reference count. Such premature freeing of kernel memory structures typically results in Use-After-Free conditions, which are among the most dangerous classes of vulnerabilities as they allow for arbitrary code execution with kernel privileges if an attacker can control the data written into the reclaimed memory region.
From a technical perspective, this issue is classified under CWE-416, commonly known as Use After Free. The root cause lies in the lack of proper reference counting and synchronization between the network device notifier chain and the thread management subsystem. When a netdevice event occurs, such as an interface going down or being removed, the system attempts to clean up associated resources. By shutting down the socket first, the kernel signals the listener task to terminate. If this termination process involves freeing memory that is still referenced by other parts of the ksmbd logic or if kthread_stop() fails to properly synchronize with the completion of the thread's exit routine due to the race condition, the integrity of the kernel heap is compromised. The fix addresses this by altering the initialization and teardown sequences. Specifically, the listener task must be created in a stopped state rather than running immediately. This ensures that no active execution context exists until it is explicitly started under controlled conditions. Furthermore, an extra reference to the task_struct is held throughout the lifecycle of the thread, ensuring that kthread_stop_put() can complete safely without the risk of the underlying memory being deallocated by concurrent operations.
The operational impact of this vulnerability is severe due to its potential for privilege escalation and system instability. An attacker with local access who can manipulate network interface states or trigger specific netdevice events could potentially exploit this race condition. By carefully timing their actions, they might force the kernel to free a task_struct that is still being accessed by another thread or interrupt context. If successful, this allows the attacker to overwrite critical kernel data structures, leading to arbitrary code execution in ring zero (kernel mode). Beyond exploitation for control takeover, even without malicious intent, this bug can cause system crashes or panics due to invalid memory accesses when the freed memory is reused and contains stale pointers. This undermines the reliability of systems running ksmbd, particularly those exposed to network environments where interface changes are frequent or controllable by unprivileged users through certain configuration manipulations.
Mitigation strategies involve both immediate patching and long-term architectural improvements. The primary mitigation is applying the upstream kernel fix that corrects the listener task lifetime management as described in the resolution notes. This includes ensuring listeners are stopped before their associated interface records are freed during TCP teardown, thereby preventing access to deallocated memory. Administrators should prioritize updating affected systems with patched versions of the Linux kernel and ksmbd components. From a defensive engineering standpoint, this incident highlights the importance of strict adherence to reference counting protocols in asynchronous event handling within the kernel. Future developments should enforce stricter synchronization primitives when dealing with thread lifecycles coupled with external hardware or network events. Additionally, enabling Kernel Hardening features such as KASAN (Kernel Address Sanitizer) during development and testing phases can help detect these types of memory corruption issues early before they reach production environments. Aligning remediation efforts with ATT&CK techniques related to privilege escalation via kernel vulnerabilities ensures that security teams monitor for indicators of exploitation attempts targeting this specific flaw in the ksmbd subsystem.