[CVE-2026-43206][IMPORTANT] drm/amdkfd: Fix out-of-bounds write in kfd_event_page_set() [ Upstream

[CVE-2026-43206][IMPORTANT] drm/amdkfd: Fix out-of-bounds write in kfd_event_page_set() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-43206
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: drm/amdkfd: Fix out-of-bounds write in kfd_event_page_set() [ Upstream
Commit: 3e04bc310d80b46eaf481f1fefcbcb37a187412d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3e04bc310d80b46eaf481f1fefcbcb37a187412d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43206
Analysis date: Thu, 30 Jul 2026 12:50:12 -0400
ActionableScore: 8
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An unprivileged local user with access to the AMD KFD device can provide an undersized event page buffer and trigger an out-of-bounds kernel memset in kfd_event_page_set(), causing kernel memory corruption with possible privilege escalation or denial of service.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-43206 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43206

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: IMPORTANT
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-43206	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-119;*CWE-20;BEST CVSS score: '7.8';DESCR 'An out-of-bounds write in the AMD KFD event page setup path occurs because kfd_event_page_set() writes KFD_SIGNAL_EVENT_LIMIT * 8 bytes without first validating that the supplied event page buffer is large enough. A local userspace process with access to the KFD device can pass a too small buffer and cause kernel memory corruption. For the CVSS the PR:L is used because exploitation requires local code execution and access to the GPU KFD interface, but it does not require full administrator privileges. The issue is not network reachable. Impact can include kernel crash and potential privilege escalation because the primitive is an out-of-bounds kernel write rather than a DoS-only failure.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) 	MAYBE	WRITE OOB SIMPLEFIX HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=8
ActionableScoreLower=7

## 1. ActionableScore

* Conservative score: 7
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  The commit explicitly says unprivileged userspace can pass a small buffer and trigger the bug.

* Memory corruption, strong corruption primitive: +2
  The bug is an out-of-bounds kernel memory write caused by memset() writing KFD_SIGNAL_EVENT_LIMIT * 8 bytes without validating the supplied size.

* Strong LPE plausibility: +2
  The primitive is a kernel OOB write from a local userspace reachable GPU/KFD path, and the commit explicitly mentions potential privilege escalation.

* Reliable kernel crash / strong DoS: +1
  Even if privilege escalation is not reliable, an OOB kernel write is sufficient for a realistic local kernel crash.

* Integrity impact plausible: +1
  Kernel memory can be overwritten beyond the intended event page buffer. Even if the memset payload is fixed, this is still a plausible kernel data integrity violation.

* Availability impact realistic: +1 for paranoid score only
  The trigger appears simple and local, so a host-wide crash is plausible. This is counted only in the paranoid score to avoid excessive double-counting with the DoS signal.

Not counted:

* Remote reachable: +0
  This is not network-triggerable.

* High-control GPU API bonus: +0
  The affected path is a GPU/KFD userspace interface, but the patch only shows size misuse. It does not show allocator shaping, callback control, refcount control, DMA ownership control, or object lifetime control beyond the OOB write itself.

* Confidentiality impact: +0
  The patch shows an OOB write, not a read-back or information disclosure primitive.

## 3. Reachability analysis

A local userspace process with access to the AMD KFD interface can trigger the bug by supplying an event page buffer smaller than KFD_SIGNAL_EVENT_LIMIT * 8. In typical deployments this likely requires access to /dev/kfd or the relevant DRM/KFD device node, but not full administrator privileges. Container impact depends on whether GPU device nodes are passed into the container. If /dev/kfd is exposed to an untrusted container or service account, the practical PR remains low. The path is not remotely reachable and depends on systems using AMDGPU/KFD functionality.

Call-site confidence: medium. The patch shows the vulnerable validation point and the commit explicitly describes the OOB write and unprivileged trigger, but the full ioctl call chain is not included in the provided input.

## 4. Severity interpretation

This behaves like an Important-class local kernel memory corruption issue, not an ordinary Moderate DoS. The realistic impact includes local kernel crash, and the patch context supports potential privilege escalation because the primitive is an out-of-bounds kernel write. Theoretical exploitability may depend on what object lies after the undersized event page buffer and how controllable the surrounding layout is, but the bug class and unprivileged reachability make auto-closure inappropriate.

## 5. One-sentence report phrase

An unprivileged local user with access to the AMD KFD device can provide an undersized event page buffer and trigger an out-of-bounds kernel memset in kfd_event_page_set(), causing kernel memory corruption with possible privilege escalation or denial of service.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is an explicitly described unprivileged out-of-bounds kernel memory write with potential privilege escalation, so it should be reviewed manually even if the exact overwrite target and exploit reliability require further analysis.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: drm/amdkfd: Fix out-of-bounds write in kfd_event_page_set() [ Upstream
Commit: 3e04bc310d80b46eaf481f1fefcbcb37a187412d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3e04bc310d80b46eaf481f1fefcbcb37a187412d

Changed files:
  drivers/gpu/drm/amd/amdkfd/kfd_events.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3e04bc310d80b46eaf481f1fefcbcb37a187412d

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-43206 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43206

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 7
  Paranoid ActionableScore: 8

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).