CVE-2026-53209: Linux Kernel Bluetooth Buffer Overflow

CVE-2026-53209 Overview

CVE-2026-53209 is a Linux kernel vulnerability in the Bluetooth hci_sync subsystem. The flaw resides in hci_adv_bcast_annoucement(), which prepends Broadcast Announcement service data to an existing extended advertising payload. When an advertising instance already holds the maximum extended advertising payload, the combined data exceeds the size of the temporary buffer used to rebuild the advertising data. The upstream fix rejects the oversized prepend operation before copying the existing payload, preserves the existing advertising data, and logs the failure through the device log.

Critical Impact
A local Bluetooth operation that triggers Broadcast Announcement prepend on a maxed-out advertising instance can overrun a kernel temporary buffer, risking kernel memory corruption and instability.

Affected Products

Linux kernel — Bluetooth hci_sync subsystem
Stable kernel branches addressed by commits 02f50e8, 10b0e83, 1338ee0, 5c65b96, cdd8bbd, and dafc9f5
Linux distributions shipping kernels prior to the backported fix

Discovery Timeline

2026-06-25 - CVE-2026-53209 published to NVD
2026-06-25 - Last updated in NVD database

Technical Details for CVE-2026-53209

Vulnerability Analysis

The Linux kernel Bluetooth stack supports extended advertising, where each advertising instance can carry a payload up to the maximum size defined by the Bluetooth specification. The hci_adv_bcast_annoucement() function prepends Broadcast Announcement service data to that payload when rebuilding advertising data inside a temporary buffer.

The vulnerable code path did not verify that the combined size of the prepended service data and the existing payload fit within the temporary buffer. When the existing instance already held the maximum extended advertising payload, the prepend operation produced data exceeding the buffer length. Copying the existing payload after the prepend caused a buffer overrun in kernel memory.

The corrective patch adds a length check before the copy. If the combined data would not fit, the function rejects the operation, leaves the existing advertising data intact, and reports the failure through the device log rather than continuing into a memory-unsafe code path.

Root Cause

The root cause is a missing boundary check in hci_adv_bcast_annoucement(). The function assumed the temporary rebuild buffer could always hold the prepended service data plus the existing extended advertising payload, an assumption that fails when the instance already carries the maximum payload size.

Attack Vector

Triggering the condition requires interaction with the Bluetooth HCI advertising configuration paths within the kernel. An actor capable of configuring extended advertising instances and invoking Broadcast Announcement prepend can drive the buffer into the oversized state. The result is kernel memory corruption in the temporary buffer, with potential consequences ranging from kernel instability and denial of service to broader memory safety impact depending on adjacent allocations.

No verified public exploitation code is available. Refer to the upstream commits listed in Kernel Git Commit 02f50e8 and Kernel Git Commit dafc9f5 for the exact code changes.

Detection Methods for CVE-2026-53209

Indicators of Compromise

Kernel device log entries from the Bluetooth subsystem reporting rejected Broadcast Announcement prepend operations after patching.
Unexpected Bluetooth HCI subsystem crashes, kernel oopses, or stack traces referencing hci_adv_bcast_annoucement or hci_sync on unpatched kernels.
Unusual configuration of extended advertising instances that consistently fill the maximum payload.

Detection Strategies

Inventory running kernel versions across Linux endpoints and servers, and compare against the fixed commits in the stable trees.
Audit Bluetooth-enabled systems where extended advertising is used, including embedded and IoT devices that ship custom kernels.
Review dmesg and journalctl -k output for Bluetooth subsystem warnings tied to advertising payload size or HCI sync failures.

Monitoring Recommendations

Forward kernel logs to a centralized logging or SIEM platform and alert on Bluetooth HCI errors and kernel panics.
Track package and kernel update status on hosts with Bluetooth radios enabled, prioritizing systems exposed to untrusted wireless environments.
Monitor for new or modified bluetoothd and HCI configurations that enable extended advertising on production systems.

How to Mitigate CVE-2026-53209

Immediate Actions Required

Apply the upstream Linux kernel fix or the vendor-provided backport that includes commit dafc9f57140e66a10945127aa7433c3d715dc253 or any of the equivalent stable-tree commits.
Reboot affected systems after kernel update to ensure the patched Bluetooth modules are loaded.
On systems that do not require Bluetooth, disable the Bluetooth service and unload the bluetooth and btusb kernel modules until patches are deployed.

Patch Information

The vulnerability is resolved upstream by adding a length check in hci_adv_bcast_annoucement() that rejects oversized Broadcast Announcement prepend operations. The fix is distributed across the following stable-tree commits: Kernel Git Commit 02f50e8, Kernel Git Commit 10b0e83, Kernel Git Commit 1338ee0, Kernel Git Commit 5c65b96, Kernel Git Commit cdd8bbd, and Kernel Git Commit dafc9f5. Consume the fix through your distribution's kernel updates.

Workarounds

Disable Bluetooth on systems where it is not required by stopping the bluetooth.service unit and blacklisting the btusb and bluetooth modules.
Avoid configuring extended advertising instances that carry the maximum payload alongside Broadcast Announcement service data until patched kernels are deployed.
Restrict physical and logical access to Bluetooth configuration interfaces to limit who can manipulate advertising instances.

bash

# Configuration example: disable Bluetooth on systems that do not require it
sudo systemctl stop bluetooth.service
sudo systemctl disable bluetooth.service
echo 'blacklist btusb' | sudo tee /etc/modprobe.d/blacklist-bluetooth.conf
echo 'blacklist bluetooth' | sudo tee -a /etc/modprobe.d/blacklist-bluetooth.conf
sudo modprobe -r btusb bluetooth