CVE-2026-90255 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: hci_conn: fix the SCO setup context lifetime
hci_setup_sync() queues a conn_handle_t with a NULL destroy callback, so the context is only freed if hci_enhanced_setup_sync() actually runs. An entry that is cancelled instead is leaked, as _hci_cmd_sync_cancel_entry() does not release entry->data when there is no destroy callback, and hci_cmd_sync_clear() cancels every pending entry when the controller is unregistered.
The context also stores a bare hci_conn pointer, so the connection can be freed while the work is queued. The dequeue in hci_conn_del() does not cover it either, as it matches on entry->data == conn and entry->data is the wrapper here. Same problem as commit 2f5d635ad590 ("Bluetooth: hci_sync: hold conn in hci_connect_acl/le_sync() callbacks").
Hold the connection and release both from a destroy callback. The submission failure path drops both, since hci_cmd_sync_submit() does not call the destroy callback when it fails to queue.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified within the Linux kernel Bluetooth subsystem centers on improper memory management and reference counting during the setup of Synchronous Connection-Oriented links. Specifically, the function hci_setup_sync queues a connection handle context that lacks a proper destruction callback mechanism. This architectural oversight means that if the subsequent enhanced synchronization step is cancelled or fails to execute before completion, the allocated context data remains in memory without being released. The cancellation routine _hci_cmd_sync_cancel_entry() relies on the presence of a destroy callback to free entry->data; when this callback is absent, as is the case here, the memory associated with the context is never reclaimed, resulting in a direct resource leak that persists until system reboot or module unload.
Beyond the immediate issue of leaked memory structures, there exists a critical use-after-free risk stemming from how connection pointers are managed within these queued contexts. The stored data contains a bare pointer to an hci_conn structure rather than a reference-counted object. Consequently, if the underlying Bluetooth connection is terminated and its associated memory freed while the work item remains queued in the system's execution pipeline, any subsequent attempt to access this context will result in dereferencing invalid memory. This scenario creates a classic use-after-free condition that can lead to kernel panics, data corruption, or potentially be exploited for arbitrary code execution depending on the state of the freed memory and the attacker's ability to influence allocation patterns.
The root cause is further compounded by deficiencies in the cleanup logic during connection teardown. The function hci_conn_del(), which handles the removal of a Bluetooth connection, attempts to dequeue pending entries by matching entry->data against the conn pointer. However, because the queued context wraps this pointer rather than storing it directly as the primary identifier for lookup purposes, the deletion routine fails to identify and remove these specific work items from the queue. This mismatch ensures that even when a connection is explicitly destroyed, its associated asynchronous tasks may remain active in the background, exacerbating both the memory leak and the use-after-free vulnerabilities described above.
This flaw aligns with CWE-401, which describes missing release of memory after effective usage, as well as CWE-416 regarding use after free conditions where a pointer is used after it has been freed due to improper lifecycle management. From an offensive security perspective, this vulnerability maps to MITRE ATT&CK technique T1203, specifically the exploitation phase involving client-side attacks or local privilege escalation vectors if triggered by malicious Bluetooth devices attempting to force connection state transitions that trigger cancellation paths without proper cleanup.
The resolution involves restructuring the context handling to ensure strict ownership and lifecycle management of both the queue entry and the underlying connection object. By holding a reference count on the hci_conn structure when it is queued, the kernel ensures that the connection remains valid for as long as any pending work depends upon it. Furthermore, implementing a dedicated destroy callback guarantees that all allocated resources are systematically released regardless of whether the operation completes successfully or is cancelled due to timeout or error conditions. This approach also addresses submission failure paths where hci_cmd_sync_submit might fail to queue an entry but must still ensure no dangling references persist in internal data structures, thereby restoring robustness to the Bluetooth stack's synchronization mechanisms and preventing both memory exhaustion and unstable kernel states caused by stale pointer dereferences.