CVE-2026-64405 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: hci_conn: Fix null ptr deref in hci_abort_conn()
hci_abort_conn() read hci_skb_event(hdev->sent_cmd) when a connection was pending, but hdev->sent_cmd can be NULL while req_status is still HCI_REQ_PEND, leading to a NULL pointer dereference and a general protection fault from the hci_rx_work() receive path.
Instead of inspecting hdev->sent_cmd, track the in-flight create connection command with a new per-connection HCI_CONN_CREATE flag and route all cancellation through hci_cancel_connect_sync(), which dispatches to a dedicated per-type cancel function. The create command is in exactly one of two states: still queued, or in flight. The cancel function holds cmd_sync_work_lock across the whole decision: the worker takes this lock to dequeue every entry, so while it is held a queued command cannot start running and an in-flight command cannot complete and let the next command become pending. This keeps the flag test and hci_cmd_sync_cancel() atomic with respect to the worker, so a queued command is simply dequeued, and an in-flight command owned by this connection is cancelled without the risk of cancelling an unrelated command that became pending in the meantime. CIS uses the same flag mechanism via HCI_CONN_CREATE_CIS but cannot be dequeued per-connection.
hci_acl_create_conn_sync() and hci_le_create_conn_sync() clear HCI_CONN_CREATE after the create command completes, but the command status handler can free conn via hci_conn_del() (for example when the controller rejects the connection) while the worker is still blocked on the connection complete event. Hold a reference on conn across the create command so the flag can be cleared without a use-after-free.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability exists within the Linux kernel's Bluetooth subsystem, specifically in the HCI (Host Controller Interface) connection management code where a null pointer dereference can occur during connection cancellation operations. The flaw manifests in the hci_abort_conn() function which attempts to access hdev->sent_cmd when a connection is in pending status but hdev->sent_cmd can legitimately be NULL while req_status remains set to HCI_REQ_PEND. This condition creates a scenario where a general protection fault occurs from the hci_rx_work() receive path, representing a critical kernel memory corruption vulnerability that could potentially lead to system crashes or privilege escalation.
The technical implementation of this vulnerability stems from an improper tracking mechanism for pending connection commands. The original code relied on inspecting hdev->sent_cmd directly which created a race condition between command queuing and cancellation operations. This approach violated fundamental principles of concurrent programming where the state of shared resources must be properly synchronized across different execution contexts. The fix implements a more robust per-connection tracking mechanism using a new HCI_CONN_CREATE flag that maintains explicit state information about whether a connection creation command is queued or actively in-flight, addressing the underlying design flaw that allowed for inconsistent state management.
The operational impact of this vulnerability extends beyond simple system stability concerns as it represents a potential attack vector that could be exploited by malicious actors to cause denial of service conditions or potentially gain elevated privileges within the kernel space. When the null pointer dereference occurs during hci_rx_work() execution, the system experiences a general protection fault which typically results in kernel panic and system crash, effectively rendering the Bluetooth functionality unusable and potentially compromising overall system availability. This vulnerability particularly affects systems with active Bluetooth connectivity where connection management operations are frequent.
The mitigation strategy involves implementing a comprehensive command tracking system that uses a dedicated per-connection HCI_CONN_CREATE flag to maintain accurate state information throughout the connection lifecycle. The solution routes all cancellation operations through hci_cancel_connect_sync() which dispatches to type-specific cancel functions, ensuring that each operation maintains atomicity with respect to worker thread execution. This approach follows established security practices by eliminating race conditions and reducing the attack surface through proper synchronization mechanisms. The implementation also includes a critical reference counting mechanism where connections maintain references across command execution to prevent use-after-free conditions during cleanup operations.
This vulnerability aligns with CWE-476 which describes null pointer dereference conditions, and represents a classic example of improper handling of asynchronous operations in kernel space. The ATT&CK framework would categorize this under privilege escalation through kernel vulnerabilities where an attacker could potentially leverage such flaws to gain elevated system privileges. The fix demonstrates adherence to secure coding principles by ensuring proper synchronization between concurrent operations and implementing robust state management mechanisms that prevent inconsistent resource access patterns. The solution also incorporates defensive programming techniques such as reference counting and atomic state transitions to ensure memory safety throughout the connection management lifecycle.
The implementation of the new flag-based tracking mechanism provides a more reliable foundation for Bluetooth connection management while maintaining backward compatibility with existing kernel interfaces. This approach prevents similar vulnerabilities from occurring in related functionality such as CIS (Connected Isochronous Stream) connections which utilize the same flag mechanism through HCI_CONN_CREATE_CIS but cannot be dequeued per-connection due to their different operational requirements. The fix ultimately strengthens the overall security posture of Linux Bluetooth implementations by addressing a fundamental flaw in command queuing and cancellation that could have been exploited in various attack scenarios involving Bluetooth device interactions.