CVE-2026-98739

What the bug is

For RFCOMM_RELEASE_ONHUP devices, rfcomm_tty_install() and __rfcomm_release_dev() both use RFCOMM_TTY_OWNED to decide who drops the initial tty_port reference. The release path tests the bit separately from the install path setting it, so both can drop that reference. The synchronous hangup does not prevent this race: port->tty is not assigned until tty_port_open(), after installation. The following interleaving is possible: 1. Install and release each obtain a reference with rfcomm_dev_get(). 2. Release observes RFCOMM_TTY_OWNED clear. 3. Install sets RFCOMM_TTY_OWNED and drops the initial reference. 4. Release drops the same initial reference again. 5. TTY cleanup drops its reference and frees the device. 6. Release performs its final tty_port_put() on the freed port. KASAN reported: BUG: KASAN: slab-use-after-free in tty_port_put+0x22/0x190 Write of size 4 at addr ffff8881001d3d5c by task poc/92 Call Trace: tty_port_put+0x22/0x190 rfcomm_dev_ioctl+0x1d4/0x1930 sock_do_ioctl+0x110/0x260 sock_ioctl+0x380/0x590 __x64_sys_ioctl+0x134/0x1c0 Allocated by task 88: rfcomm_dev_ioctl+0x8f6/0x1930 sock_do_ioctl+0x110/0x260 sock_ioctl+0x380/0x590 __x64_sys_ioctl+0x134/0x1c0 Freed by task 65: kfree+0x131/0x3c0 rfcomm_dev_destruct+0x23b/0x2f0 release_one_tty+0xc1/0x370 process_one_work+0x661/0x1090 Use test_and_set_bit() in both paths so that only the caller that changes RFCOMM_TTY_OWNED from clear to set drops the initial reference. Each path keeps its own lookup reference until release or TTY cleanup, preserving the existing callback ordering and error handling.

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.

net/bluetooth/rfcomm/tty.c

What this is

BLUETOOTH SUBSYSTEMMAINTAINERS section matched on net/bluetooth/ · linux-bluetooth@vger.kernel.org · Supported

Kernel module

rfcomm

Check it on the machine

grep -wE 'CONFIG_BT|CONFIG_BT_RFCOMM|CONFIG_BT_RFCOMM_TTY' /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 rfcomm

Prints 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

M

a module where it is built at all; some flavours do not build it

Build switches

CONFIG_BT, CONFIG_BT_RFCOMM, CONFIG_BT_RFCOMM_TTY

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

2026-10-18 (today)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

not scored

CISA KEV

not listedthe KEV catalogue

Debian urgency

not yet assignedsource

Subsystem

net/bluetooth

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
3.15	6.12.113	a03ccf1ab773
3.15	6.18.56	0a554901bd22
3.15	7.2.10	e5aa7fbf7a44
3.15	7.3	2d696c1ed346