VulnerabilityPublished 18 Oct 2026Updated 21 Oct 2026

CVE-2026-98809: Linux kernel · Bluetooth: hci_sync: don't drain cmd_sync backlog on unregister

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c : update Linux kernel when convenient.

Data as of 26 Oct 2026, 13:07 UTC

Severity

Unrated

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 5% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c, b11acfcb5925ed27fae692b27931a1ac732677fb, b1f24c1ab52345e810c42a1a81286cb5a7c92252 +2

Exploitation evidence

Disclosed: evidence found.
CVE published 18 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 008ee9eb8a11bcabf12c91771dd4f470b082bd44, < e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c	Fixed in e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c
LinuxLinux	Affected ≥ 008ee9eb8a11bcabf12c91771dd4f470b082bd44, < b11acfcb5925ed27fae692b27931a1ac732677fb	Fixed in b11acfcb5925ed27fae692b27931a1ac732677fb
LinuxLinux	Affected ≥ 008ee9eb8a11bcabf12c91771dd4f470b082bd44, < b1f24c1ab52345e810c42a1a81286cb5a7c92252	Fixed in b1f24c1ab52345e810c42a1a81286cb5a7c92252
LinuxLinux	Affected ≥ 008ee9eb8a11bcabf12c91771dd4f470b082bd44, < 143bde97c4101ae68eb656c87e620c45b07a3090	Fixed in 143bde97c4101ae68eb656c87e620c45b07a3090
LinuxLinux	Affected ≥ 008ee9eb8a11bcabf12c91771dd4f470b082bd44, < 7f16443a30f4e86d84ae4faf057d333b41ddb757	Fixed in 7f16443a30f4e86d84ae4faf057d333b41ddb757
LinuxLinux	Affected =5.17	Fixed in–

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 any request still waiting with -ENODEV before cancelling the work. The entries left over are destroyed with -ECANCELED by the existing sweep in hci_cmd_sync_clear(). They stay on the list until the work has stopped, so hci_cmd_sync_dequeue() and friends still see them. A callback already running may still issue another command, which delays unregister by at most one timeout per remaining command, not by the whole backlog.

References

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