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CVE-2026-63856
drm/amdgpu/vcn: set no_user_fence for VCN v2.0 enc/dec rings
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/gpu. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-63856 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| 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 e2b5499fca55f1a32960a311bbb62e35891eaf73)
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_v2_0.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.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
- 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
- M
- a module where it is built at all; some flavours do not build it
- 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
- not yet assignedsource
- 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 |
|---|---|---|
| 5.3 | 6.6.141 | f264019be80d |
| 5.3 | 6.12.91 | 5e777bc4cbe9 |
| 5.3 | 6.18.33 | ac06ce5cac9e |
| 5.3 | 7.0.10 | c71aecae98e4 |
| 5.3 | 7.1 | 8d80b293b41f |
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 a crafted AMDGPU_CS ioctl to a local DRM render node (/dev/dri/renderD*); the vulnerable VCN v2.0 path is not reachable over the network.
- AC:LAttack complexity, low
- An attacker with render-node access can reliably submit a VCN DEC/ENC command stream with an AMDGPU_CHUNK_ID_FENCE user-fence chunk; no race or victim-specific timing is required beyond having a VCN 2.0-capable AMDGPU.
- PR:LPrivileges required, low
- Any unprivileged local user who can open the DRM render node (typical render-group membership on Linux desktops, or any app granted GPU access on RDNA1 systems) can trigger the bug without root or capabilities.
- UI:NUser interaction, none
- No victim interaction is needed; the attacker directly crafts and submits the malicious command submission via the AMDGPU DRM ioctl interface.
- S:UScope, unchanged
- The misdirected GPU fence write is constrained to the attacker's own GPU virtual address space via per-process amdgpu_vm page tables; impact remains within the same kernel/OS security authority, not a VM-guest-to-host or IOMMU-boundary escape.
- C:HConfidentiality impact, high
- The unsupported 64-bit user fence causes the VCN engine to perform a misdirected GPU memory write (40-bit address truncation on the decoder ring), which is memory corruption that can be leveraged to corrupt adjacent GPU buffers and disclose their prior contents when read back.
- I:HIntegrity impact, high
- The VCN hardware performs a GPU-initiated write of the fence sequence to a potentially mis-targeted GPU virtual address, providing a memory-corruption write primitive within the submitter's GPU mappings that could be chained for further exploitation.
- A:HAvailability impact, high
- Submitting an unsupported user fence to VCN rings can hang the video engine or trigger a GPU fault/reset (amdgpu_gpu_reset), denying GPU service to all local consumers including the display stack.