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CVE-2026-64557
Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()
Published 2026-07-29 (3 months ago) by the Linux kernel CNA. Subsystem include/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-64557 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4720-1 · 2026-08-05 · text | 6.1.180-1 | Update the kernel and reboot. DLA-4720-1 shipped the fix on 2026-08-05, in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6405-1 · 2026-07-31 · text | 6.12.100-1 | Update the kernel and reboot. DSA-6405-1 shipped the fix on 2026-07-31, in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
l2cap_sock_new_connection_cb() returned l2cap_pi(sk)->chan after release_sock(parent). Once the parent lock is dropped the newly enqueued child socket sk is reachable via the accept queue, so another task can accept and free it before the callback dereferences sk, resulting in a use-after-free. Rework the ->new_connection() op so the core, rather than the callback, owns the child channel's lifetime. The op now receives a pre-allocated new_chan and returns an errno instead of allocating and returning a channel. l2cap_new_connection() allocates the child channel and links it into the conn list via __l2cap_chan_add() before invoking the callback, so the conn-list reference keeps the channel alive once release_sock(parent) exposes the socket to other tasks. Channel configuration that was duplicated in l2cap_sock_init() and the various new_connection callbacks is consolidated into l2cap_chan_set_defaults(), which now inherits from the parent channel when one is supplied.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
include/net/bluetooth/l2cap.h
net/bluetooth/6lowpan.c
net/bluetooth/l2cap_core.c
net/bluetooth/l2cap_sock.c
net/bluetooth/smp.c
- What this is
- BLUETOOTH SUBSYSTEMMAINTAINERS section matched on include/net/bluetooth/ · linux-bluetooth@vger.kernel.org · Supported
- Kernel module
- bluetooth_6lowpan
Check it on the machine
grep -wE 'CONFIG_BT|CONFIG_BT_6LOWPAN' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w bluetooth_6lowpanPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, s390x/s390x
- bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_BT, CONFIG_BT_6LOWPAN
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-07-29 (3 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- adjacent network (AV:A)source
- EPSS
- 0.24%, higher than 14.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- include/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 3.13 | 6.1.178 | b39298044e55 |
| 3.13 | 6.6.145 | 8c37e4338c80 |
| 3.13 | 6.12.97 | 84e718b6a814 |
| 3.13 | 6.18.40 | 36da806f7fba |
| 3.13 | 7.1.5 | 733e76e74e40 |
| 3.13 | 7.2 | 6fef032af009 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DLA-4723-1 | 2026-08-07 | bullseye 6.1.180-1~deb11u1 | tracker |
| DLA-4720-1 | 2026-08-05 | bookworm 6.1.180-1 | tracker |
| DSA-6405-1 | 2026-07-31 | trixie 6.12.100-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:AAttack vector, adjacent network
- The vulnerable callback is reached only from L2CAP signalling handlers (`l2cap_connect`, `l2cap_le_connect_req`, `l2cap_ecred_conn_req`, `l2cap_connect_cfm`) processing connection requests received from a remote Bluetooth peer. Bluetooth radio range constitutes an adjacent network.
- AC:LAttack complexity, low
- The attacker drives one side of the race by sending unlimited L2CAP connect requests and can induce the other side, since the local daemon accepts (immediately, for DEFER_SETUP listeners) and closes rejected/unauthorized children; on SMP the accepting task runs truly concurrently while the callback is still inside `release_sock()`, so the window is hit reliably with repeated attempts.
- PR:NPrivileges required, none
- `l2cap_connect()` bypasses the link-mode and encryption-key-size checks entirely for PSM 0x0001 (SDP), where bluetoothd holds a listening L2CAP socket, so an unpaired and unauthenticated remote device can reach `l2cap_sock_new_connection_cb()`; LE CoC and low-security BR/EDR listeners are likewise reachable without credentials.
- UI:NUser interaction, none
- Incoming L2CAP connection requests are processed automatically by the kernel and accepted by the always-running Bluetooth daemon with no victim action, no pairing prompt, and no user confirmation.
- S:UScope, unchanged
- The corrupted `l2cap_chan`/`sock` objects and the resulting memory corruption are confined to the kernel's own security authority, with no crossing of a VM, IOMMU, or sandbox boundary.
- C:HConfidentiality impact, high
- This is a use-after-free: the freed `l2cap_chan` slab object can be reallocated with attacker-groomed data and its fields are subsequently read back and transmitted to the attacker via the connect response and `l2cap_build_conf_req()`, and `__l2cap_chan_add()` deposits kernel list pointers into the reallocated object, giving a kernel-memory disclosure primitive.
- I:HIntegrity impact, high
- After the free, `l2cap_connect()`/`l2cap_le_connect_req()` write attacker-supplied PSM, SCID, MTU/MPS and BD_ADDR values plus list pointers into the freed object, and `__set_chan_timer()` arms delayed work whose function pointers live in that freed memory — a controlled write primitive suitable for heap spraying and control-flow hijack.
- A:HAvailability impact, high
- Even without successful exploitation, the use-after-free reads and writes into freed slab memory and links a dead object into the conn list, reliably producing kernel oops/panic and corrupted list traversal on subsequent L2CAP operations.