CVE-2026-98809
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:
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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.
Technical details traces, logs and code from the original report
INFO: task syz-executor:5749 blocked for more than 143 seconds. cancel_work_sync hci_cmd_sync_clear hci_unregister_dev vhci_release
CVSS
NVD hasn't assigned a CVSS score to this CVE (common since the April 2026 policy change).
Exploitation probability (EPSS)
- Probability of exploitation in the next 30 days
- 0.17 %
- Percentile among all scored CVEs
- 6
- Score date
- 10/20/2026
EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).
Affected technologies (1)
⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.
References
Show 4 references
Raw JSON (NVD)
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{
"id": "CVE-2026-98809",
"cveTags": [],
"metrics": {},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "008ee9eb8a11bcabf12c91771dd4f470b082bd44",
"lessThan": "143bde97c4101ae68eb656c87e620c45b07a3090",
"versionType": "git"
},
{
"status": "affected",
"version": "008ee9eb8a11bcabf12c91771dd4f470b082bd44",
"lessThan": "7f16443a30f4e86d84ae4faf057d333b41ddb757",
"versionType": "git"
},
{
"status": "affected",
"version": "008ee9eb8a11bcabf12c91771dd4f470b082bd44",
"lessThan": "e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c",
"versionType": "git"
},
{
"status": "affected",
"version": "008ee9eb8a11bcabf12c91771dd4f470b082bd44",
"lessThan": "b1f24c1ab52345e810c42a1a81286cb5a7c92252",
"versionType": "git"
}
],
"programFiles": [
"net/bluetooth/hci_sync.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "5.17"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "5.17",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "6.12.113",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.56",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.2.10",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"net/bluetooth/hci_sync.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-10-18T16:17:34.997",
"references": [
{
"url": "https://git.kernel.org/stable/c/143bde97c4101ae68eb656c87e620c45b07a3090",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/7f16443a30f4e86d84ae4faf057d333b41ddb757",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/b1f24c1ab52345e810c42a1a81286cb5a7c92252",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Received",
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nBluetooth: hci_sync: don't drain cmd_sync backlog on unregister\n\nhci_unregister_dev() disables cmd_work and cmd_timer, then calls\nhci_cmd_sync_clear(), whose cancel_work_sync() waits for\nhci_cmd_sync_work() to return. That worker dequeues and runs every\nentry on cmd_sync_work_list. With cmd_work disabled nothing reaches\nthe controller, so each queued HCI command waits the full\nHCI_CMD_TIMEOUT (2s).\n\nThe backlog has no bound. Userspace can keep queuing MGMT commands\nsuch as MGMT_OP_GET_CLOCK_INFO against a controller that doesn't\nanswer. Closing /dev/vhci then blocks in vhci_release() for\nbacklog * 2s:\n\n INFO: task syz-executor:5749 blocked for more than 143 seconds.\n cancel_work_sync\n hci_cmd_sync_clear\n hci_unregister_dev\n vhci_release\n\nIn a local reproduction the backlog held more than 5000 entries,\nwhich comes to hours of hang.\n\nStop the worker from taking new entries once HCI_UNREGISTER is set,\nand wake any request still waiting with -ENODEV before cancelling\nthe work. The entries left over are destroyed with -ECANCELED by the\nexisting sweep in hci_cmd_sync_clear(). They stay on the list until\nthe work has stopped, so hci_cmd_sync_dequeue() and friends still see\nthem. A callback already running may still issue another command,\nwhich delays unregister by at most one timeout per remaining command,\nnot by the whole backlog."
}
],
"lastModified": "2026-10-19T10:19:44.937",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}