The Linux kernel now tracks CVE-2025-40289 — a deterministic crash in the AMDGPU DRM driver where VRAM sysfs attributes remain visible on GPUs that have no dedicated VRAM (APUs/integrated GPUs), and reading those attributes can cause a kernel crash; upstream stable commits have been merged to hide those attributes when they are not present and avoid the fault.
Modern Linux graphics stacks expose a variety of runtime metrics via sysfs under /sys/class/drm//device/ to help tooling and diagnostics: things like mem_info_vram_used and related VRAM counters are common. On systems with discrete AMD GPUs, those attributes represent real VRAM accounting structures managed by the kernel. On integrated GPUs (APUs) there is sometimes no dedicated VRAM manager to back those sysfs attributes; a recent change in upstream driver behavior exposed a window where the sysfs entries could still be read even though the underlying manager was not initialized. That read path could dereference uninitialized structures and crash the kernel. The NVD and multiple vulnerability trackers summarize the fix as “drm/amdgpu: hide VRAM sysfs attributes on GPUs without VRAM” and link upstream stable commits that remove or hide the attributes when they are not applicable. The flaw is not a remote attack vector; it is a local, user-triggerable availability bug. Any process with read access to those sysfs nodes can trigger the error (for example, with cat /sys/class/drm/card/device/mem_infovram*). Because it is a kernel crash primitive, the primary operational impact is Denial‑of‑Service: driver oops, compositor crashes, session loss, or a full machine reboot in the worst cases. Upstream kernel patches apply a simple guard: hide or suppress VRAM sysfs attributes on GPUs that do not expose VRAM, or check manager initialization before attempting to access manager structures.
Operators who follow that sequence — inventory, vendor patching, reboot, verify — remove the risk. Those who defer or fail to inventory exposed images risk avoidable downtime or targeted disruption.
Conclusion: apply the kernel updates that include the upstream stable commits that hide or guard VRAM sysfs attributes on GPUs without VRAM, restrict sysfs/device exposure in the meantime, and treat inventory/embedded vendor kernels as the highest long‑tail risk. Preserving kernel oops traces and confirming package changelogs are the essential verification steps to close the case.
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / Overview
Modern Linux graphics stacks expose a variety of runtime metrics via sysfs under /sys/class/drm//device/ to help tooling and diagnostics: things like mem_info_vram_used and related VRAM counters are common. On systems with discrete AMD GPUs, those attributes represent real VRAM accounting structures managed by the kernel. On integrated GPUs (APUs) there is sometimes no dedicated VRAM manager to back those sysfs attributes; a recent change in upstream driver behavior exposed a window where the sysfs entries could still be read even though the underlying manager was not initialized. That read path could dereference uninitialized structures and crash the kernel. The NVD and multiple vulnerability trackers summarize the fix as “drm/amdgpu: hide VRAM sysfs attributes on GPUs without VRAM” and link upstream stable commits that remove or hide the attributes when they are not applicable. The flaw is not a remote attack vector; it is a local, user-triggerable availability bug. Any process with read access to those sysfs nodes can trigger the error (for example, with cat /sys/class/drm/card/device/mem_infovram*). Because it is a kernel crash primitive, the primary operational impact is Denial‑of‑Service: driver oops, compositor crashes, session loss, or a full machine reboot in the worst cases. Upstream kernel patches apply a simple guard: hide or suppress VRAM sysfs attributes on GPUs that do not expose VRAM, or check manager initialization before attempting to access manager structures. Technical anatomy — what went wrong
Where the failure occurs
- The offending path is in the AMDGPU DRM driver sysfs show handlers for VRAM accounting attributes. Those handlers call into the VRAM/TTM resource accounting routines to compute usage values.
- After a previous kernel change removed a “dummy VRAM manager” for certain APU/IGP configurations, the VRAM manager pointer is left uninitialized for GPUs that truly have no VRAM. If the sysfs show routine is still reachable and tries to use that manager, it ends up dereferencing NULL or an uninitialized pointer inside kernel space. The result is a kernel oops.
The patch approach
Upstream maintainers chose a conservative, low‑risk remediation path: avoid exposing VRAM sysfs attributes when the underlying manager is absent, or add explicit early checks before any manager fields are read. This turns a forced kernel fault into a safe no-op (the sysfs entry can either be hidden or return a benign default/value indicating “not available”). The change is intentionally small — a surgical guard — which is exactly the kind of fix that is straightforward to backport into stable kernels and vendor packages. The kernel stable tree contains commits addressing this exact behavior.Exposure, exploitability and practical impact
Attack vector and privileges required
- Attack vector: Local. Any process that can read the relevant sysfs paths on the host can trigger the crash. On many desktop and workstation systems these paths are world-readable or accessible to users in common groups (video/render), so the practical privilege requirement is often low. In containerized environments where /sys/class/drm or /dev/dri is mounted into containers, untrusted containers can likewise exercise the path.
Likelihood and impact
- Likelihood: The condition is simple to trigger if the system exposes the sysfs attributes and the underlying VRAM manager is uninitialized. A single read (for example, a monitoring script or a cat command) is sufficient.
- Impact: Availability — a kernel oops, driver reset, compositor crash, or session termination. The practical operational impact can be severe for shared infrastructure: CI runners, virtual desktop servers, multi-user workstations, or cloud images that expose GPU devices to tenants. There is no authoritative public evidence that the bug directly leads to privilege escalation or remote code execution; however, kernel crash primitives are dangerous and may be used in escalation chains in certain contexts. Treat the issue as an availability-first security priority for exposed hosts.
Who should worry most
- Shared GPU hosts (CI runners, multi-tenant GPU cloud instances)
- VDI and kiosk environments with many untrusted user sessions
- Embedded or OEM devices where vendor kernels lag upstream (long-tail risk)
- Developer machines and desktops that run untrusted code or mount sysfs in permissive ways
Detection, logging and forensics
How a triggered crash looks
Kernel oopses will appear in dmesg and journalctl -k and will reference amdgpu symbols and the failure site. Typical operational indicators include:- Kernel oops entries mentioning amdgpu or ttm/VRAM manager functions
- Repeated compositor crashes (Wayland/Xwayland) correlated with reading sysfs
- Driver reset watchdogs and pageflip timeouts tied to GPU workloads
Quick detection checklist (operational)
- Inventory kernels and module state: uname -r; lsmod | grep amdgpu.
- Inspect the sysfs attributes: ls -l /sys/class/drm/card/device/mem_infovram and verify permissions.
- Search kernel logs for amdgpu oops: journalctl -k --no-pager | grep -i amdgpu.
- Preserve logs before rebooting when triaging an incident.
Mitigation and remediation — practical playbook
Definitive remediation (recommended)
- Install vendor/distribution kernel updates that include the upstream stable commit(s) that hide or guard VRAM sysfs attributes. Reboot the host to activate the fix (kernel code changes require a reboot). Confirm the package changelog or vendor advisory explicitly references the fix/commit.
Short-term compensations (when immediate patching is not possible)
- Restrict access to the sysfs paths that are the trigger: use udev rules or group membership changes to prevent untrusted users or containers from reading sysfs VRAM counters. For example, change ownership of /sys/class/drm//device/mem_infovram to root:adm or a trusted group and remove world-read permission.
- Avoid mounting /sys/class/drm or /dev/dri into untrusted containers or CI runners. Remove GPU passthrough to untrusted guests.
- If GPU acceleration is non‑essential on a host, consider blacklisting amdgpu temporarily (note: this disables GPU acceleration and can break sessions).
Validation after patching
- Reboot into the patched kernel.
- Re-run representative display workloads (video playback, compositor operations, hot‑plug) and read the previously problematic sysfs entries (if you must) from a secure account to confirm they either do not exist or do not crash the kernel. Plan a 24–72 hour validation window depending on risk appetite.
Example udev rule (concept)
- Create a udev rule that restricts access to DRM device nodes and the problematic sysfs entries to a trusted group. This reduces surface area while you schedule kernel updates.
Verification and cross‑checks operators must perform
- Confirm the running kernel package’s changelog includes one of the upstream stable commit hashes referenced in public trackers. NVD/OSV lists the kernel stable commits for this CVE; vendors typically include those commits in package changelogs when backporting.
- If you run custom kernels, cherry‑pick the upstream patch into your tree, rebuild, and test on representative hardware (especially on machines with integrated GPUs).
Critical analysis — strengths, limitations and residual risks
Strengths of the response
- The upstream fix is narrow and defensive: hiding unused sysfs attributes or adding an early initialization check is a low-risk change that preserves normal functionality for discrete GPUs. That makes it an excellent candidate for rapid backporting to stable kernels and vendor packages.
- Multiple independent vulnerability trackers (NVD, OSV, distribution security pages) and upstream commits converge on the same diagnosis and remediation steps, which increases confidence that the correct root cause has been identified and fixed.
Residual and systemic risks
- Long‑tail vendor kernels and embedded images: appliances, OEM devices, or deeply embedded Linux images often lag upstream by months. These are the most persistent exposure vectors because vendors may delay or omit backports. This is the single largest operational risk for this class of kernel bugs.
- Inventory gaps: organizations that do not map which images or VMs include amdgpu-enabled kernels may overlook carriers of the vulnerable code. A narrow upstream attestation (for example, a vendor saying “we checked product X”) is authoritative only for that product; absence of an attestation is not proof of absence. Operators must verify locally.
- Attack surface in containers and passthrough: even if userland in a container looks harmless, the host kernel is what matters. A patched container image does not protect you if the host kernel is unpatched and exposes the vulnerable sysfs nodes. Remove /sys/class/drm and /dev/dri mounts from untrusted containers.
What remains unverifiable or uncertain
- CVSS and public exploit status: At the time of writing, NVD has recorded the CVE and referenced upstream commits, but a definitive, globally‑agreed CVSS score for CVE-2025-40289 was not yet published on the NVD entry; tracking mirrors differ in how they present the severity. Treat numeric scores as triage guidance — prioritize by exposure in your environment instead.
- Privilege escalation risk: public advisories and vendors classify this as an availability (DoS) weakness; there is no authoritative public evidence that the bug itself leads to privilege escalation or remote code execution. Whether a kernel crash primitive can be composed with other bugs to escalate privileges depends on local kernel hardening, memory layout, and other factors — that is inherently scenario-specific and not conclusively verifiable from the public metadata alone. Flag this as a cautionary but unproven escalation risk.
Operational checklist for system administrators (ordered actions)
- Inventory: Run uname -r and lsmod | grep amdgpu to identify candidate hosts. List /sys/class/drm and note permissions.
- Consult vendor advisories: Check your distribution/security tracker for CVE-2025-40289 and fixed kernel package versions. If using vendor kernels (RHEL, SUSE, Ubuntu, Debian, Oracle), prefer vendor updates.
- Patch and reboot: Install the updated kernel package and plan a reboot window; kernel fixes require reboot to take effect.
- If patching is delayed, apply mitigations: restrict sysfs/device node access via udev, remove /dev/dri from untrusted containers, consider blacklisting the amdgpu module on low-risk hosts where GPU acceleration is nonessential.
- Validate: After reboot, run representative display and workload tests; monitor dmesg/journalctl for recurrence for 24–72 hours.
Why operators should act now
- The exploit is trivial to trigger from a local account with read access to sysfs; in multi‑tenant or shared environments that makes it a reliable disruption tool. Deterministic DoS bugs in kernel drivers are operationally useful to attackers targeting CI runners, VDI hosts, and shared developer systems. Multiple distributions and upstream patches exist, so remediation is straightforward — but the operational work remains in inventorying and deploying updates at scale. Treat the fix as a high-priority operational update for exposed hosts.
Final verdict and recommendations
CVE-2025-40289 is a classic example of a small defensive lapse in kernel driver code — exposing sysfs attributes that are not always backed by initialized kernel objects — with outsized operational consequences. The remedy is tiny, low-risk, and widely accepted: hide or guard VRAM sysfs attributes on GPUs that have no VRAM and verify manager initialization before any reads. Distributions and the upstream stable tree have already absorbed the change, so the practical actions for administrators are clear: inventory, patch, reboot, and apply short-term access controls where immediate patching is not possible. Because the vulnerability is local and availability-focused, prioritize remediation by exposure (multi-tenant hosts, CI runners, VDI, and embedded fleets) rather than raw CVSS alone. Preserve kernel logs when triaging, validate package changelogs for the upstream commits, and escalate to vendors for embedded/OEM kernels that lag upstream.Operators who follow that sequence — inventory, vendor patching, reboot, verify — remove the risk. Those who defer or fail to inventory exposed images risk avoidable downtime or targeted disruption.
Conclusion: apply the kernel updates that include the upstream stable commits that hide or guard VRAM sysfs attributes on GPUs without VRAM, restrict sysfs/device exposure in the meantime, and treat inventory/embedded vendor kernels as the highest long‑tail risk. Preserving kernel oops traces and confirming package changelogs are the essential verification steps to close the case.
Source: MSRC Security Update Guide - Microsoft Security Response Center
