CVE-2026-98773

What the bug is

acm_port_shutdown() is called from the tty-port machinery whenever the last user closes the port. acm_disconnect() sets acm->disconnected and calls tty_port_tty_vhangup(), which eventually triggers port_shutdown(). At that point acm_disconnect() has already called acm_poison_urbs() and is about to free the control and read URBs. However, acm_port_shutdown() unconditionally calls acm_unpoison_urbs() and, when the ALWAYS_POLL_CTRL quirk is set, immediately re-submits the ctrlurb and all read URBs. If the concurrent acm_disconnect() then frees those URBs and their DMA buffers while they are in-flight, the result is a use-after-free in acm_ctrl_irq() or acm_read_bulk_callback() accessing the freed DMA memory. Fix by checking acm->disconnected after draining the delayed anchor and returning early: if we are in a disconnect path the URBs must remain poisoned and must not be resubmitted. The early return is placed after the delayed-anchor drain loop because that loop only cancels write-side accounting (wb->use = false and autopm counter) and does not touch the hardware path.

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.

drivers/usb/class/cdc-acm.c

What this is

USB ACM DRIVERMAINTAINERS section matched on drivers/usb/class/cdc-acm.* · linux-usb@vger.kernel.org · Maintained

Kernel module

cdc_acm

Check it on the machine

grep -wE 'CONFIG_OF|CONFIG_PCI|CONFIG_USB|CONFIG_USB_ACM|CONFIG_USB_GADGET|CONFIG_USB_PHY|CONFIG_USB_PRINTER|CONFIG_USB_SUPPORT|CONFIG_USB_TMC|CONFIG_USB_WDM' /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 cdc_acm

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/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/cloud-arm64, i386/686, i386/686-pae, i386/rt/686-pae, ppc64el/powerpc64le
• trixieMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/cloud-arm64, armel/rpi, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, s390x/s390x
• forky, sidMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt-amd64, arm64/cloud-arm64, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, s390x/s390x

M

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

Build switches

CONFIG_OF, CONFIG_PCI, CONFIG_USB, CONFIG_USB_ACM, CONFIG_USB_GADGET, CONFIG_USB_PHY, CONFIG_USB_PRINTER, CONFIG_USB_SUPPORT, CONFIG_USB_TMC, CONFIG_USB_WDM

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

drivers/usb

Upstream fixes

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

Introduced	Fixed in	Commit
6.12.83	6.12.113	9742905d9ed5
6.18.24	6.18.56	a0ed07b5bbb2
7.1	7.2.10	420ca35af891
7.1	7.3	dc614d6bc991
6.1.175	0	0
6.6.136	0	0
6.19.14	0	0
7.0.1	0	0