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CVE-2026-64042
vfio/pci: Check BAR resources before exporting a DMABUF
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/vfio. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64042 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
A DMABUF exports access to BAR resources and, although they are requested at startup time, we need to ensure they really were reserved before exporting. Otherwise, it's possible to access unreserved resources through the export. Add a check to the DMABUF-creation 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/vfio/pci/vfio_pci_dmabuf.c
- What this is
- VFIO DRIVERMAINTAINERS section matched on drivers/vfio/ · kvm@vger.kernel.org · Maintained
- Kernel module
- vfio_pci_core
Check it on the machine
grep -wE 'CONFIG_VFIO|CONFIG_VFIO_PCI_CORE|CONFIG_VFIO_PCI_DMABUF' /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 vfio_pci_corePrints 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. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidMnot built on armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- ?
- not established - no Makefile entry for the affected file
- M
- a module where it is built at all; some flavours do not build it
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_VFIO, CONFIG_VFIO_PCI_CORE, CONFIG_VFIO_PCI_DMABUF
- 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
- 2026-07-19 (3 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.14%, higher than 3.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/vfio
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.19 | 7.0.11 | 8443cd4497a4 |
| 6.19 | 7.1 | 702809dabdec |
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:LAttack vector, local
- The bug is reached only through the VFIO_DEVICE_FEATURE ioctl on an open VFIO PCI device file descriptor; there is no network, adjacent-radio, or physical-bus entry point to this code.
- AC:LAttack complexity, low
- An attacker with VFIO access can deterministically issue VFIO_DEVICE_FEATURE_DMA_BUF GET requests and probe BAR region indices; when a BAR failed reservation/mapping at enable time, export succeeds without races or attacker-uncontrollable timing.
- PR:LPrivileges required, low
- Exploitation requires access to a VFIO-assigned PCI device (ioctl on /dev/vfio/* or /dev/vfio/devices/*), which is routinely delegated to unprivileged tenants in GPU passthrough/cloud and documented unprivileged VFIO deployments, not init-namespace root.
- UI:NUser interaction, none
- No victim interaction is required beyond the attacker already holding a VFIO device fd; triggering dma-buf export is a direct ioctl by the attacker process.
- S:CScope, changed
- Exporting an unreserved BAR bypasses VFIO’s BAR reservation/iomap gate and exposes MMIO for peer-to-peer DMA via dma-buf/iommufd/RDMA importers, crossing the IOMMU/DMA security boundary that normal VFIO BAR read/write/mmap paths enforce.
- C:HConfidentiality impact, high
- The exported dma-buf yields P2P DMA read access to MMIO physical addresses of BAR regions VFIO deliberately did not reserve, enabling disclosure of device registers and sensitive MMIO-backed state beyond the authorized VFIO mapping path.
- I:HIntegrity impact, high
- P2P DMA writes through the exported dma-buf can modify MMIO of an unreserved BAR and alter device behavior (including triggering further device DMA side effects), giving a high-integrity write primitive outside the intended VFIO access controls.
- A:HAvailability impact, high
- Unauthorized MMIO access via P2P DMA to unreserved BAR resources can hang or crash device drivers, trigger platform instability during reset/FLR windows, and cause kernel oops/panics from conflicting host/device MMIO use.