CVE-2026-64539 Bluetooth: eir: Fix stack OOB write when prepending the Flags AD
A local attacker with CAP_NET_ADMIN can trigger a stack out-of-bounds write in the Linux kernel Bluetooth subsystem, potentially leading to code execution or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-64539?
CVE-2026-64539 is a high-severity memory corruption vulnerability in Linux, published on 27 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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.
Weakness: CWE-121
Which versions are affected by CVE-2026-64539?
How do I fix CVE-2026-64539?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-64539 being exploited?
There is no known exploitation of CVE-2026-64539 in the wild and no public exploit code.
Sources
Also known as AZL-94061, BELL-CVE-2026-64539, DEBIAN-CVE-2026-64539, GHSA-rxg5-jr9r-8pc7, ROOT-OS-DEBIAN-12-CVE-2026-64539, UBUNTU-CVE-2026-64539.