CVE-2026-98809

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: hci_sync: don't drain cmd_sync backlog on unregister

hci_unregister_dev() disables cmd_work and cmd_timer, then calls

hci_cmd_sync_clear(), whose cancel_work_sync() waits for

hci_cmd_sync_work() to return. That worker dequeues and runs every

entry on cmd_sync_work_list. With cmd_work disabled nothing reaches

the controller, so each queued HCI command waits the full

HCI_CMD_TIMEOUT (2s).

The backlog has no bound. Userspace can keep queuing MGMT commands

such as MGMT_OP_GET_CLOCK_INFO against a controller that doesn't

answer. Closing /dev/vhci then blocks in vhci_release() for

backlog * 2s:

INFO: task syz-executor:5749 blocked for more than 143 seconds.

cancel_work_sync

hci_cmd_sync_clear

hci_unregister_dev

vhci_release

In a local reproduction the backlog held more than 5000 entries,

which comes to hours of hang.

Stop the worker from taking new entries once HCI_UNREGISTER is set,

and wake a

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References