---
id: CVE-2026-64539
title: 'Bluetooth: eir: Fix stack OOB write when prepending the Flags AD'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  Bluetooth: eir: Fix stack OOB write when prepending the Flags AD

  eir_create_adv_data() builds the advertising data into a fixed-size
  buffer ("size", 31 for the legacy …
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= b44133ff03be30b55f23036e62f403a3f7784fce <
    0f0b6232af56441d0a2dcb173cc4f8d8aab39014
  - >-
    Linux >= b44133ff03be30b55f23036e62f403a3f7784fce <
    09301f1fdf2aef8cce34d0c4650c30e7edb1ced9
  - >-
    Linux >= b44133ff03be30b55f23036e62f403a3f7784fce <
    f1b4df9c260c51726da2e86e19322825fddeefd0
  - >-
    Linux >= b44133ff03be30b55f23036e62f403a3f7784fce <
    57077eeb586c42f124bc09e018449362223067b3
  - >-
    Linux >= b44133ff03be30b55f23036e62f403a3f7784fce <
    6f5fb689fdf80bdd143f22a502f9eb1f3c85e286
  - Linux 4.1
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T15:42:00.875042Z'
published: '2026-07-27'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:52:50.860Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-64539'
references:
  - url: 'https://git.kernel.org/stable/c/0f0b6232af56441d0a2dcb173cc4f8d8aab39014'
  - url: 'https://git.kernel.org/stable/c/09301f1fdf2aef8cce34d0c4650c30e7edb1ced9'
  - url: 'https://git.kernel.org/stable/c/f1b4df9c260c51726da2e86e19322825fddeefd0'
  - url: 'https://git.kernel.org/stable/c/57077eeb586c42f124bc09e018449362223067b3'
  - url: 'https://git.kernel.org/stable/c/6f5fb689fdf80bdd143f22a502f9eb1f3c85e286'
tags:
  - cve.org
epss: 0.00122
epssPercentile: 0.01818
ingestedAt: '2026-10-16T17:24:46.830Z'
---

## Overview

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

Bluetooth: eir: Fix stack OOB write when prepending the Flags AD

eir_create_adv_data() builds the advertising data into a fixed-size
buffer ("size", 31 for the legacy path). It may prepend a 3-byte "Flags"
AD structure (LE_AD_NO_BREDR on an LE-only controller) and then copies
the per-instance data without checking that it still fits:

	memcpy(ptr, adv->adv_data, adv->adv_data_len);

tlv_data_max_len() only reserves those 3 bytes when the user-supplied
flags carry a managed-flags bit, so an instance added with flags == 0 is
accepted with adv_data_len up to the full buffer. At advertise time the
flags are still prepended, and the memcpy() writes 3 + adv_data_len
bytes into the size-byte buffer:

  BUG: KASAN: stack-out-of-bounds in eir_create_adv_data (net/bluetooth/eir.c:301)
  Write of size 31 at addr ffff88800a547bdc by task kworker/u9:0/65
  Workqueue: hci0 hci_cmd_sync_work
   __asan_memcpy (mm/kasan/shadow.c:106)
   eir_create_adv_data (net/bluetooth/eir.c:301)
   hci_update_adv_data_sync (net/bluetooth/hci_sync.c:1310)
   hci_schedule_adv_instance_sync (net/bluetooth/hci_sync.c:1817)
   hci_cmd_sync_work (net/bluetooth/hci_sync.c:332)
  This frame has 1 object:
   [32, 64) 'cp'

The "Flags" structure is added by the kernel, not requested by
userspace, so only prepend it when it fits together with the instance
advertising data; when there is no room for both, drop the flags rather
than the user-provided data.

Reachable by a local user with CAP_NET_ADMIN owning an LE-only
controller on the legacy advertising path.

## Affected

- `Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < 0f0b6232af56441d0a2dcb173cc4f8d8aab39014`
- `Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < 09301f1fdf2aef8cce34d0c4650c30e7edb1ced9`
- `Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < f1b4df9c260c51726da2e86e19322825fddeefd0`
- `Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < 57077eeb586c42f124bc09e018449362223067b3`
- `Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < 6f5fb689fdf80bdd143f22a502f9eb1f3c85e286`
- `Linux 4.1`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.