CVE-2026-90015

What the bug is

When a TD reaches a link TRB with data that is not aligned to the endpoint's wMaxPacketSize, xhci_align_td() stages the unalignable tail through the bounce buffer of the ring segment holding that link TRB. xhci_unmap_td_bounce_buffer() later unmaps it and, for IN transfers, copies the data back into the URB's buffer. The enqueue path records the segment that was bounced in td->bounce_seg, under the assumption that a TD never spans more than two ring segments. That assumption does not hold: a TD large enough to span three or more segments crosses several link TRBs and can be bounced at each of them. Only the last one survives in td->bounce_seg, so every earlier bounce buffer is neither copied back nor DMA unmapped. The URB still completes with actual_length equal to the requested length and no error, so the transfer looks successful while a wMaxPacketSize sized hole in the destination buffer silently keeps its previous contents. It also leaks a DMA mapping per dropped bounce. Any sufficiently large and fragmented bulk transfer can hit this. It was found with a USB mass storage device behind xHCI backing a dm-verity target with 512 byte hash blocks, where the stale data is detected rather than silently consumed. The device enumerates as SuperSpeed, so wMaxPacketSize is 1024, while dm-bufio issues one 512 byte bio per hash block. verity_prefetch_io() makes the block layer merge hundreds of them into a single request of up to 512 scatterlist entries of 512 bytes each. At 256 TRBs per ring segment such a TD spans three segments, and every segment boundary falls on an odd multiple of 512, i.e. unaligned to wMaxPacketSize. dm-bufio then caches a hash block holding stale data and dm-verity declares the metadata block corrupted: device-mapper: verity: 8:2: metadata block 10850 is corrupted A reproducer running this under qemu is available at https://github.com/baloo/xhci-verity The bounce state (bounce_buf, bounce_dma, bounce_len, bounce_offs) already lives on the ring segment, so there is nothing extra to track. Keep recording the last bounced segment in td->bounce_seg and, on completion, walk the segments from td->start_seg up to it, unmapping every segment that still has a pending bounce. Stopping at td->bounce_seg rather than td->end_seg matters: a bounce implies the TD continues past that segment's link TRB, so bounce_seg is always strictly before end_seg, and a later TD may already have started in end_seg and been bounced there. Walking that far would copy a foreign bounce buffer into this URB and unmap it twice. It also keeps the walk correct if a TD ever wraps the whole ring so that end_seg == start_seg. [mn: Add ring->num_segs check to prevent unlikely infinite for loop.]

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/host/xhci-ring.c

What this is

USB XHCI DRIVERMAINTAINERS section matched on drivers/usb/host/xhci* · linux-usb@vger.kernel.org · Supported

Check it on the machine

grep -wE 'CONFIG_OF|CONFIG_PCI|CONFIG_USB|CONFIG_USB_EHCI_HCD|CONFIG_USB_FHCI_HCD|CONFIG_USB_FOTG210_HCD|CONFIG_USB_FSL_USB2|CONFIG_USB_GADGET|CONFIG_USB_ISP116X_HCD|CONFIG_USB_ISP1362_HCD|CONFIG_USB_MAX3421_HCD|CONFIG_USB_OHCI_HCD|CONFIG_USB_PCI|CONFIG_USB_PHY|CONFIG_USB_R8A66597_HCD|CONFIG_USB_SL811_HCD|CONFIG_USB_SUPPORT|CONFIG_USB_U132_HCD|CONFIG_USB_UHCI_HCD|CONFIG_USB_XEN_HCD|CONFIG_USB_XHCI_HCD' /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_EHCI_HCD, CONFIG_USB_FHCI_HCD, CONFIG_USB_FOTG210_HCD, CONFIG_USB_FSL_USB2, CONFIG_USB_GADGET, CONFIG_USB_ISP116X_HCD, CONFIG_USB_ISP1362_HCD, CONFIG_USB_MAX3421_HCD, CONFIG_USB_OHCI_HCD, CONFIG_USB_PCI, CONFIG_USB_PHY, CONFIG_USB_R8A66597_HCD, CONFIG_USB_SL811_HCD, CONFIG_USB_SUPPORT, CONFIG_USB_U132_HCD, CONFIG_USB_UHCI_HCD, CONFIG_USB_XEN_HCD, CONFIG_USB_XHCI_HCD

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

2026-09-16 (33 days ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.21%, higher than 10.5% 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
4.8	5.10.270	c8124b28f12d
4.8	5.15.221	e04d5304a248
4.8	6.1.188	a1629dfb0114
4.8	6.6.157	43239fc6dfb6
4.8	6.12.110	3c9a2b5a4f11
4.8	6.18.51	efaab8938fb9
4.8	7.2.5	7236bbd2cb7d
4.8	7.3	ff44dfb03a29

Debian advisories