CVE-2026-98697 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
USB: serial: fix dynamic id driver deregistration race
Only free the dynamic ids after having deregistered the driver and removed the "new_id" attribute to avoid leaking any id added by a racing write to the attribute.
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Analysis
by VulDB Data Team • 10/19/2026
The Linux kernel USB serial subsystem contains a critical synchronization flaw related to the lifecycle management of dynamically allocated device identifiers, specifically within the context of driver registration and deregistration processes. This vulnerability arises from an improper ordering of operations during module unload or driver detachment sequences. When a USB serial driver is being removed, it must unregister itself from the core kernel infrastructure and subsequently clean up any resources that were dynamically created for specific devices. The flaw lies in the fact that prior to this fix, the code path attempted to free dynamic identifier structures before fully deregistering the driver interface and removing the sysfs new_id attribute file. This sequence creates a race condition window where external actors or kernel subsystems can interact with the partially dismantled driver state.
The operational mechanism of this vulnerability exploits the asynchronous nature of user-space interactions with kernel interfaces via sysfs. The new_id attribute allows users to dynamically bind specific USB device IDs to the serial driver at runtime without recompiling the kernel. If a process writes to this attribute while the driver is in the midst of being unloaded, it can trigger an allocation or binding operation on data structures that are already scheduled for deallocation but not yet fully removed from the active lookup tables. Because the dynamic ID list was freed before the new_id interface was disabled and the driver deregistered, a concurrent write could result in accessing memory that has been returned to the kernel's allocator pool. This constitutes a use-after-free scenario where stale pointers are dereferenced or modified after their underlying storage has been reclaimed by other parts of the system.
From a security perspective, this race condition falls under CWE-416: Use After Free and CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). The vulnerability allows for potential denial-of-service conditions through kernel panics or crashes if the freed memory is overwritten by other allocations before the invalid access occurs. More critically, in certain configurations, this could lead to arbitrary code execution if an attacker can control the contents of the reclaimed memory slab and trigger specific dereference paths that execute shellcode or pivot privilege escalation vectors. The ATT&CK framework categorizes such kernel-level race conditions under techniques involving exploitation of software vulnerabilities for initial access or persistence, specifically leveraging improper input validation and synchronization errors to destabilize the operating system core.
The impact of this vulnerability is significant because USB serial drivers are commonly used in embedded systems, IoT devices, and industrial control environments where physical access to ports may be available to adversaries. An attacker with local user privileges could exploit this race condition by rapidly writing new device IDs while simultaneously triggering driver unload operations through automated scripts or fuzzing tools. The resulting instability can cause system-wide crashes, leading to service disruption in critical infrastructure. Furthermore, the unpredictability of memory reuse means that successful exploitation is highly dependent on timing and heap state, making it a challenging but viable target for sophisticated attackers aiming to gain kernel-level control over compromised systems.
To mitigate this vulnerability, users must ensure their Linux kernels are updated with patches that correct the deregistration sequence in the USB serial subsystem. The fix enforces strict ordering by ensuring that the driver is completely deregistered and the new_id sysfs attribute is removed before any dynamic ID structures are freed from memory. This eliminates the window of opportunity for race conditions to occur during module unloading. System administrators should apply security updates promptly, particularly on systems where USB devices are frequently connected or disconnected dynamically. Additionally, implementing strict access controls on sysfs interfaces can reduce the attack surface by limiting which userspace processes can trigger dynamic binding operations, thereby adding a layer of defense-in-depth against exploitation attempts targeting kernel synchronization flaws.