CVE-2026-98456 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: mgmt: fix race in read_unconf_index_list()
read_unconf_index_list() counts unconfigured controllers before allocating its response, then checks the device flags again while filling it.
hci_dev_list_lock stabilizes list membership, but it does not serialize the per-device flags. During asynchronous controller setup, the worker can set HCI_UNCONFIGURED and clear HCI_SETUP between the two passes. A controller omitted from the allocation count can then become eligible for the fill pass, causing an out-of-bounds write to rp->index[].
Allocate space for every device on hci_dev_list. Since list membership cannot change while hci_dev_list_lock is held, the response remains large enough regardless of flag transitions. The reported count and response length still include only eligible unconfigured controllers.
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Analysis
by VulDB Data Team • 10/18/2026
The vulnerability identified in the Linux kernel Bluetooth management subsystem represents a classic race condition arising from improper synchronization between list traversal and state inspection. Specifically, the function read_unconf_index_list() is responsible for enumerating Bluetooth controllers that are currently unconfigured to generate a response for management interface queries. The flaw lies in the sequence of operations performed during this enumeration process. Initially, the code counts the number of unconfigured devices by iterating through the device list while holding the hci_dev_list_lock. This lock ensures that the structural integrity and membership of the list remain stable during the counting phase. However, after determining the count, the function allocates a response buffer based on this figure before proceeding to populate it with specific details about each controller.
The critical technical flaw occurs in the gap between allocating memory and filling the data structure. While the hci_dev_list_lock protects against changes to the list itself, such as devices being added or removed from the chain, it does not serialize access to the per-device flags associated with each Bluetooth adapter. During asynchronous controller setup operations, a worker thread can modify these internal state flags concurrently. Specifically, there is a window where a device might transition its status by setting the HCI_UNCONFIGURED flag and clearing the HCI_SETUP flag between the initial counting pass and the subsequent filling pass. Because the lock does not protect these individual flags, this race condition allows a controller that was previously excluded from the count to become eligible for inclusion during the fill phase.
This discrepancy leads directly to an out-of-bounds write vulnerability within the kernel memory space. Since the response buffer rp->index[] is allocated strictly based on the initial count of unconfigured controllers, any device that becomes eligible after this allocation but before or during the population process will cause the code to attempt writing beyond the bounds of the allocated array. This type of memory corruption can lead to system instability, kernel panics, or potentially be exploited for privilege escalation if an attacker can influence the timing of these asynchronous setup events. The vulnerability highlights a common pitfall in concurrent programming where structural locks are mistaken for comprehensive state synchronization mechanisms.
From a classification perspective, this issue aligns with CWE-362, which describes concurrent execution using shared resources with insufficient synchronization. It also relates to CWE-190, indicating an integer overflow or wraparound that results in the allocation of insufficient memory relative to the actual data size required. In terms of attack vectors and tactics, this vulnerability could be leveraged within the context of MITRE ATT&CK techniques related to privilege escalation via kernel exploitation. An attacker with local access might exploit this race condition to corrupt kernel memory structures, potentially gaining control over execution flow or accessing restricted system resources that are normally protected by higher-level security boundaries.
The mitigation implemented in the Linux kernel addresses this root cause by fundamentally changing how memory is allocated for the response buffer. Instead of relying on a dynamic count derived from a snapshot-in-time iteration, the updated code allocates space sufficient to accommodate every device present on the hci_dev_list at any given time. By holding the hci_dev_list_lock during both the allocation and population phases, or by ensuring that the maximum possible size is reserved regardless of transient flag states, the system guarantees that the response buffer remains large enough even if flags transition asynchronously. This approach decouples memory sizing from volatile state checks, thereby eliminating the possibility of an out-of-bounds write caused by race conditions in device status updates.
To further mitigate similar vulnerabilities in future developments or related subsystems, developers should adhere to strict locking hierarchies that encompass all shared mutable state accessed during a single logical operation. It is essential to distinguish between locks that protect structural data integrity and those required for protecting atomicity of complex state transitions. In this specific case, relying on the maximum theoretical size rather than dynamic counting provides a robust defense against timing-based exploits. Regular static analysis and concurrency testing tools should be employed to detect such race conditions early in the development lifecycle, ensuring that kernel subsystems remain resilient against asynchronous interference from worker threads or interrupt handlers.