[CVE-2026-74716][MODERATE REGULAR] accel/amdxdna: Fix locally exploitable BUG_ON in amdxdna_insert_pages() [ Upstream

[CVE-2026-74716][MODERATE REGULAR] accel/amdxdna: Fix locally exploitable BUG_ON in amdxdna_insert_pages() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74716
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: accel/amdxdna: Fix locally exploitable BUG_ON in amdxdna_insert_pages() [ Upstream
Commit: 13339132d89d00b513dff0730bff3a313b9b13b5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=13339132d89d00b513dff0730bff3a313b9b13b5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74716
Analysis date: Sat, 22 Aug 2026 17:04:07 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Borderline manual review
Manual review required: NO

Summary:
A local unprivileged process with access to the amdxdna device node can trigger a predictable BUG_ON through the GEM mmap fault path after MADV_DONTNEED, causing a kernel denial of service without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-74716 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74716

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: MODERATE REGULAR
Manual review required: NO

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-2026-74716	MODERATE	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:N/I:N/A:H';CWE-617;CWE-754;CWE-703;BEST CVSS score: '5.5';DESCR 'A locally reachable BUG_ON can be triggered in the amdxdna GEM mmap path when amdxdna_insert_pages() maps a non imported GEM object with VM_MIXEDMAP and normal system memory backing. A local userspace process can mmap the object, call madvise(MADV_DONTNEED), and then access the mapping again so the shmem fault path reaches vmf_insert_pfn() with a valid PFN and a VM_MIXEDMAP VMA. This predictably hits the kernel assertion and can crash the system, resulting in denial of service. For the CVSS the PR:L is used because a local user or process must be able to access the amdxdna DRM or accel device node and create the affected mapping. The issue is not network reachable. Impact is availability loss only because the patch context shows a reachable assertion rather than UAF, OOB access, or an arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Borderline manual review (with actual score 3)  SKIP CVE-2026-74716 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	READ SIMPLEFIX DMAorINTERRUPT MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Borderline manual review**

## 2. Signal breakdown

* Local unprivileged trigger: +1
  The commit explicitly states that an unprivileged userspace process can mmap a non imported GEM object, call MADV_DONTNEED, and access the mapping again.

* Reliable kernel crash / strong DoS: +1
  The path predictably reaches an explicit BUG_ON in vmf_insert_pfn_prot when VM_MIXEDMAP is set and pfn_valid(pfn) is true.

* Availability impact realistic: +1 in paranoid score only
  The crash appears reliable on affected systems exposing the amdxdna device node, but this mostly overlaps with the BUG_ON DoS signal.

* Rare AND hardware dependent exposure: -1 in conservative score
  The affected path requires AMD XDNA accel hardware and the amdxdna driver/device node to be present and accessible.

No memory corruption, UAF, OOB write, arbitrary write, refcount takeover, callback control, or page-cache ownership bypass is supported by the patch.

## 3. Reachability analysis

A local userspace process with access to the amdxdna DRM/accel device node can trigger the bug. This is PR:L in CVSS-like terms because local code execution and device-node access are required, but root or CAP_SYS_ADMIN is not implied by the commit. Namespaces or containers matter only if the device node is passed through to the container. The path is not network reachable. Exposure is limited to systems with the affected AMD XDNA accelerator driver and accessible device nodes.

Call-site confidence: high. The commit message describes the concrete mmap, MADV_DONTNEED, fault, vmf_insert_pfn, and BUG_ON path.

## 4. Severity interpretation

This behaves like an ordinary Moderate local denial-of-service issue rather than an Important-class vulnerability. The theoretical impact is a kernel crash through a reachable assertion. Realistic exploitation evidence supports availability impact only. There is no supported privilege escalation primitive and no evidence of confidentiality or integrity impact.

## 5. One-sentence report phrase

A local unprivileged process with access to the amdxdna device node can trigger a predictable BUG_ON through the GEM mmap fault path after MADV_DONTNEED, causing a kernel denial of service without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a locally exploitable kernel BUG_ON with reliable DoS on affected hardware, but the patch supports availability impact only and does not show a memory corruption or privilege escalation primitive.

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

Patch: accel/amdxdna: Fix locally exploitable BUG_ON in amdxdna_insert_pages() [ Upstream
Commit: 13339132d89d00b513dff0730bff3a313b9b13b5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=13339132d89d00b513dff0730bff3a313b9b13b5

Changed files:
  drivers/accel/amdxdna/amdxdna_gem.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=13339132d89d00b513dff0730bff3a313b9b13b5

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

The original Linux kernel CVE announcement for CVE-2026-74716 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74716

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:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 2
  Paranoid ActionableScore: 3

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: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).