CVE-2026-98737 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: hci_sync: Fix inquiry cache use-after-free
The sync command worker holds hdev->req_lock, but inquiry-cache updates and flushes use hdev->lock. Both hci_acl_create_conn_sync() and hci_stop_discovery_sync() look up entries and read their fields without taking hdev->lock.
After either lookup returns, a concurrent HCIINQUIRY ioctl can acquire hdev->lock and flush the cache, freeing the entry. The worker then reads the freed entry while preparing a create-connection or remote-name-cancel command. The list traversal also races with cache updates and removal.
KASAN reported these accesses:
BUG: KASAN: slab-use-after-free in hci_acl_create_conn_sync+0x5f1/0x650 Workqueue: hci0 hci_cmd_sync_work Call Trace: hci_acl_create_conn_sync+0x5f1/0x650 hci_cmd_sync_work+0x13c/0x290
Allocated by task 90: hci_inquiry_cache_update+0x3e6/0x7d0 hci_inquiry_result_evt+0x3cb/0x560
Freed by task 93: hci_inquiry_cache_flush+0x111/0x2b0 hci_inquiry+0x2f2/0x780 hci_sock_ioctl+0x269/0x5f0
BUG: KASAN: slab-use-after-free in hci_stop_discovery_sync+0x3b1/0x3c0 Workqueue: hci0 hci_cmd_sync_work Call Trace: hci_stop_discovery_sync+0x3b1/0x3c0 hci_cmd_sync_work+0x173/0x300
Allocated by task 86: hci_inquiry_cache_update+0x483/0x940 hci_inquiry_result_evt+0x3cb/0x560
Freed by task 91: hci_inquiry_cache_flush+0x13e/0x2f0 hci_inquiry+0x2f2/0x780 hci_sock_ioctl+0x269/0x5f0
Hold hdev->lock across each lookup and all reads from its result. Copy the remote address before unlocking so discovery cancellation does not retain a cache entry pointer. Release the lock before sending synchronous HCI commands, since their completion handlers may need the same lock.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel Bluetooth subsystem contains a critical synchronization flaw within the hci_sync module that results in use-after-free vulnerabilities during inquiry operations. This issue stems from an inconsistent locking strategy where different code paths utilize distinct mutexes to protect shared data structures, specifically the device's inquiry cache. The synchronous command worker thread operates under the protection of hdev->req_lock when managing connection requests and discovery states. However, updates to and flushes of the inquiry cache are guarded by a separate lock, hdev->lock. This architectural mismatch creates a race condition window where data integrity cannot be guaranteed because concurrent threads can access or modify the same memory regions without mutual exclusion relative to one another.
The operational impact manifests when functions such as hci_acl_create_conn_sync and hci_stop_discovery_sync perform lookups on inquiry cache entries. These functions read fields from these entries while holding only req_lock, leaving them vulnerable to concurrent modifications by other threads that hold lock. Specifically, a user-space application triggering an HCIINQUIRY ioctl can initiate a cache flush operation via the kernel's socket interface. This action acquires hdev->lock and proceeds to free the inquiry cache entry in question. If this occurs while the synchronous command worker is still processing the previously looked-up reference, the worker will attempt to read from or manipulate memory that has already been deallocated by the slab allocator.
Kernel Address Sanitizer (KASAN) reports confirm these use-after-free conditions within hci_acl_create_conn_sync and hci_stop_discovery_sync. The call traces indicate that entries are allocated during inquiry result event processing via hci_inquiry_cache_update but freed prematurely through hci_inquiry_cache_flush triggered by the ioctl handler. This race condition allows an attacker to potentially exploit the dangling pointer for arbitrary code execution or denial of service, depending on how the kernel handles the corrupted memory access and whether further exploitation primitives are available in the surrounding context. The vulnerability affects system stability and security posture by allowing local privilege escalation or system crashes through crafted Bluetooth stack interactions.
To mitigate this vulnerability, developers must enforce strict locking consistency across all accesses to the inquiry cache. The fix involves holding hdev->lock during both the lookup phase and any subsequent reads of the retrieved entry fields within the synchronous command worker context. It is essential to copy the remote address data from the cached structure before releasing the lock to ensure that discovery cancellation or other concurrent operations do not invalidate pointers retained by the worker thread. Furthermore, the lock must be released prior to sending synchronous HCI commands because their completion handlers may also require access to hdev->lock, preventing potential deadlocks while maintaining memory safety during the critical window between lookup and command execution. This adjustment aligns with standard concurrency control practices recommended in CWE-362 for concurrent execution race conditions and addresses the improper synchronization identified in ATT&CK techniques related to kernel exploitation vectors.