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CVE-2026-63851
drm/amdgpu/vcn: set no_user_fence for VCN v4.0.5 enc ring
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/gpu. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-63851 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 | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
VCN encoder and decoder rings do not support 64-bit user fence writes, reject CS submissions with user fences. (cherry picked from commit 084d94ac93707bdda07efb5cee786f632de4219b)
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/gpu/drm/amd/amdgpu/vcn_v4_0_5.c
- What this is
- RADEON and AMDGPU DRM DRIVERSMAINTAINERS section matched on drivers/gpu/drm/amd/ · amd-gfx@lists.freedesktop.org · Supported
- Kernel module
- amdgpu
Check it on the machine
grep -w CONFIG_DRM_AMDGPU /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 amdgpuPrints 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 1 release, so nothing is claimed about those.
- bookworm?
- trixieMnot built on amd64/cloud-amd64, arm64/cloud-arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, s390x/s390x
- forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, 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 switch
- CONFIG_DRM_AMDGPU
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
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.18%, higher than 6.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/gpu
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.7 | 6.12.91 | 75091030f07b |
| 6.7 | 6.18.33 | 6d9a98c5ed65 |
| 6.7 | 7.0.10 | 7f23b5c420b9 |
| 6.7 | 7.1 | 589a254bf3e8 |
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
- Exploitation requires submitting AMDGPU command streams via the DRM render node (DRM_IOCTL_AMDGPU_CS), which is a local ioctl/device-file interface with no network-facing entry point.
- AC:LAttack complexity, low
- An attacker with render-node access can deterministically craft a CS submission with a FENCE chunk targeting the VCN_ENC ring; no race conditions or attacker-uncontrollable timing are required.
- PR:LPrivileges required, low
- The only gate is access to /dev/dri/renderD* (DRM_AUTH|DRM_RENDER_ALLOW), which is available to unprivileged local users in the render/video group and does not require root or capabilities obtainable only in the init namespace.
- UI:NUser interaction, none
- Once the attacker has render-node access, triggering the bug requires no additional victim interaction beyond normal GPU command submission.
- S:UScope, unchanged
- Impact is confined to the same local security domain (kernel/GPU driver); exploitation does not cross a VM, container, or IOMMU security boundary to a different authority.
- C:HConfidentiality impact, high
- The unsupported GPU fence operation causes the VCN hardware to perform DMA writes outside the driver's validated semantics, creating a memory-corruption primitive that could expose or corrupt GPU-mapped memory beyond the intended 8-byte fence slot.
- I:HIntegrity impact, high
- The bug enables GPU-initiated writes to attacker-chosen GPU virtual addresses (user fence buffer), and hardware misbehavior on unsupported fence commands can corrupt adjacent or shared dma-buf memory with unpredictable write patterns.
- A:HAvailability impact, high
- Submitting unsupported user fences to the VCN ring can hang the GPU, trigger VCN poison/RAS interrupts, or crash the graphics subsystem, causing denial of service on affected systems.