CVE-2026-90055

What the bug is

syzbot reported a shift-out-of-bounds in __vcc_connect(): UBSAN: shift-out-of-bounds in net/atm/common.c:382:32 shift exponent -1 is negative CPU: 0 UID: 0 PID: 5987 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026 Call Trace: <TASK> dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 ubsan_epilogue+0xa/0x30 lib/ubsan.c:233 __ubsan_handle_shift_out_of_bounds+0x36d/0x400 lib/ubsan.c:494 __vcc_connect+0x14b4/0x19c0 net/atm/common.c:382 vcc_connect+0x328/0x8f0 net/atm/common.c:498 pvc_bind+0x272/0x380 net/atm/pvc.c:52 __sys_bind+0x2e3/0x410 net/socket.c:1976 __x64_sys_bind+0x7a/0x90 net/socket.c:1979 ... ATM device ci_range fields (vpi_bits and vci_bits) represent the number of bits supported for VPI and VCI addressing on the device. net/atm/common.c directly uses these fields as bit shift counts: vpi >> dev->ci_range.vpi_bits vci >> dev->ci_range.vci_bits 1 << vcc->dev->ci_range.vpi_bits 1 << vcc->dev->ci_range.vci_bits usbatm_atm_init() sets ci_range.vpi_bits and ci_range.vci_bits to ATM_CI_MAX (-1), which is defined in <uapi/linux/atmdev.h> as a sentinel value for userspace ATM_SETCIRANGE requests, not a valid bit count. Shifting by -1 is undefined behavior and triggers UBSAN warnings. ATM UNI cell headers allow up to 8 bits for VPI (0..255) and 16 bits for VCI (0..65535). Initialize vpi_bits to 8 and vci_bits to 16, as done by solos-pci.

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/atm/usbatm.c

What this is

ALCATEL SPEEDTOUCH USB DRIVERMAINTAINERS section matched on drivers/usb/atm/usbatm.c · linux-usb@vger.kernel.org · Maintained

Kernel module

none to look for. The file would have gone into usbatm, and Debian does not compile it into that module, so finding usbatm in lsmod would say nothing about this CVE.

Check it on the machine

grep -wE 'CONFIG_OF|CONFIG_PCI|CONFIG_USB|CONFIG_USB_ATM|CONFIG_USB_GADGET|CONFIG_USB_PHY|CONFIG_USB_SPEEDTOUCH|CONFIG_USB_SUPPORT' /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.

Show whether Debian builds this, per release

Debian does not build this code. In 5 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.

• bookworm, trixie, forky, sid, bookworm · linux-6.12n

n

not enabled on any flavour - this release does not build the code

Build switches

CONFIG_OF, CONFIG_PCI, CONFIG_USB, CONFIG_USB_ATM, CONFIG_USB_GADGET, CONFIG_USB_PHY, CONFIG_USB_SPEEDTOUCH, CONFIG_USB_SUPPORT

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

2026-09-17 (31 days ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.21%, higher than 10.6% of all CVEssource

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
2.6.13	5.10.270	8442586526c4
2.6.13	5.15.221	561cbd6d4902
2.6.13	6.1.188	76bc7c3a4485
2.6.13	6.6.157	7baa0c92be39
2.6.13	6.12.110	1e964d414bfd
2.6.13	6.18.52	ff7f77a234f7
2.6.13	7.2.6	756677031151
2.6.13	7.3	a60fd8c6dbaa

Debian advisories