CVE-2026-46218: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-46218 Overview

CVE-2026-46218 affects the Linux kernel's AMD GPU driver (drm/amdgpu). The uvd, vce, and vcn code paths access the Indirect Buffer (IB) at predefined offsets without validating that the IB is large enough to contain those offsets. The ib_get_value and ib_set_value helpers performed no bounds checking, and the index variable was previously signed, allowing arithmetic overflow to bypass any size comparison. The upstream fix introduces explicit bounds checking and changes the index type to uint32_t to prevent overflow from defeating the validation. This is a kernel-level memory safety issue [CWE-125 / CWE-787] in the AMD GPU command submission path.

Critical Impact
Missing bounds validation in amdgpu IB access can lead to out-of-bounds reads or writes within kernel memory, potentially causing kernel crashes (denial of service) or memory corruption on systems using AMD GPUs.

Affected Products

Linux kernel — drm/amdgpu driver (UVD, VCE, VCN command submission code)
Systems with AMD GPUs relying on the affected kernel video acceleration paths
Linux distributions shipping the unpatched upstream kernel revisions

Discovery Timeline

2026-05-28 - CVE-2026-46218 published to NVD
2026-05-28 - Last updated in NVD database

Technical Details for CVE-2026-46218

Vulnerability Analysis

The Linux kernel AMD GPU driver uses Indirect Buffers (IBs) to submit command streams to the UVD (Unified Video Decoder), VCE (Video Compression Engine), and VCN (Video Core Next) hardware blocks. The driver reads and writes specific DWORD offsets inside an IB to parse commands and patch parameters such as buffer addresses and sizes.

The helper functions ib_get_value and ib_set_value accepted an index into the IB without verifying that the index fell within the allocated IB length. When the IB submitted by a user space client was shorter than the offsets the driver assumed, the access reached beyond the allocation boundary. A separate flaw stems from the index variable being a signed integer that could overflow, causing a naive size comparison to evaluate as true even for out-of-range offsets.

Root Cause

The root cause is missing input validation on attacker-controlled command buffer sizes combined with an integer overflow weakness in the indexing logic. The driver trusted that the IB length matched the layout expected by uvd, vce, and vcn parsers. The upstream patches add length checks inside ib_get_value and ib_set_value and convert idx to uint32_t. Callers must now handle arbitrary return values when the index is out of range.

Attack Vector

Exploitation requires the ability to submit GPU command buffers, typically via the DRM render node ioctl interface on a system with an AMD GPU. A local user with access to /dev/dri/renderD* can craft an undersized or malformed IB to trigger the out-of-bounds access in kernel context. The most likely outcome is a kernel oops resulting in denial of service. Memory corruption scenarios depend on adjacent kernel allocations and downstream caller behavior. See the upstream fixes for technical detail: Linux Kernel Commit 0fb5cb55, Linux Kernel Commit 66085e20, Linux Kernel Commit a853178d, Linux Kernel Commit ee26fcf7, and Linux Kernel Commit fec8b11b.

No verified public proof-of-concept code is available. The fixes are merged upstream; refer to the commits above for the canonical implementation.

Detection Methods for CVE-2026-46218

Indicators of Compromise

Kernel oops or panic messages referencing amdgpu, uvd_v*, vce_v*, or vcn_v* in dmesg or /var/log/kern.log.
Unexpected GPU reset events (amdgpu: GPU reset begin!) following user-mode rendering or media decode workloads.
Repeated DRM ioctl failures from unprivileged processes attempting to submit command streams.

Detection Strategies

Monitor kernel ring buffer output for crash signatures inside amdgpu_uvd_*, amdgpu_vce_*, or amdgpu_vcn_* symbols.
Audit which local users and containers can access /dev/dri/renderD* device nodes, since access is a prerequisite for triggering the flaw.
Compare running kernel versions and AMD GPU module build IDs against vendor advisories listing fixed releases.

Monitoring Recommendations

Forward kernel logs and audit records to a centralized log platform to identify repeated amdgpu faults across the fleet.
Alert on kernel taint flag changes (/proc/sys/kernel/tainted) that indicate a recent oops or warning.
Track GPU driver crash telemetry from endpoint agents and correlate with the process that issued the offending DRM ioctl.

How to Mitigate CVE-2026-46218

Immediate Actions Required

Inventory Linux hosts with AMD GPUs and identify those running kernel versions that predate the fix commits.
Apply the distribution kernel update that incorporates the upstream drm/amdgpu bounds-checking patches and reboot affected systems.
Restrict local access to DRM render nodes so that only trusted users and workloads can submit GPU command buffers.

Patch Information

The vulnerability is resolved upstream by adding bounds checking to ib_get_value and ib_set_value and converting the index to uint32_t. The fix is distributed across the following stable commits: 0fb5cb55, 66085e20, a853178d, ee26fcf7, and fec8b11b. Consume the patched kernel from your Linux distribution rather than back-porting individually when possible.

Workarounds

Tighten permissions on /dev/dri/renderD* and /dev/dri/card* to limit local users who can issue DRM ioctls.
Disable the amdgpu module on systems that do not require AMD GPU acceleration by blacklisting it in /etc/modprobe.d/.
For container hosts, avoid passing GPU device nodes into untrusted containers until the kernel is patched.

bash

# Verify the kernel version and check whether the amdgpu module is loaded
uname -r
lsmod | grep amdgpu

# Restrict access to DRM render nodes to the 'render' group only
ls -l /dev/dri/
sudo chgrp render /dev/dri/renderD*
sudo chmod 0660 /dev/dri/renderD*

# Optional: blacklist amdgpu where GPU acceleration is not required
echo 'blacklist amdgpu' | sudo tee /etc/modprobe.d/disable-amdgpu.conf
sudo update-initramfs -u