CVE-2026-98809 Linux CVE debrief

Who should care

Linux kernel developers and maintainers, Bluetooth device manufacturers, and users of Linux-based systems with Bluetooth capabilities should be aware of this vulnerability and take steps to mitigate its effects. This includes reviewing and applying patches, monitoring system logs, and implementing measures to limit the number of HCI commands that can be queued.

Why it matters

A vulnerability in the Linux kernel's Bluetooth hci_sync component can cause a denial-of-service condition when a large backlog of HCI commands accumulates, leading to a prolonged system hang.

• Denial-of-service condition due to HCI command backlog accumulation
• Prolonged system hang or freeze
• Potential for exploitation through specially crafted HCI commands

Technical summary

The vulnerability is caused by the HCI command synchronization backlog not being properly drained during device unregistration, leading to a potential denial-of-service condition. The HCI command synchronization backlog is not properly drained during device unregistration, leading to a potential denial-of-service condition. This can result in a significant delay in system response times, potentially leading to a prolonged system hang or freeze. The vulnerability affects Linux kernel developers and maintainers, Bluetooth device manufacturers, and users of Linux-based systems with Bluetooth capabilities.

Defensive priority

Medium

Recommended defensive actions

• Review and apply the provided patches to the Linux kernel to fix the vulnerability
• Monitor system logs for signs of HCI command backlog accumulation
• Implement measures to limit the number of HCI commands that can be queued
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The vulnerability is caused by the HCI command synchronization backlog not being properly drained during device unregistration, leading to a potential denial-of-service condition. The issue is further complicated by the fact that userspace can keep queuing MGMT commands against a controller that doesn't answer, leading to a backlog with no bound. In a local reproduction, the backlog held more than 5000 entries, which comes to hours of hang. To verify this issue, defenders should review system logs for signs of HCI command backlog and

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.