[CVE-2026-68427][MODERATE 7.0] gpu: host1x: Fix use-after-free in host1x_bo_clear_cached_mappings [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-68427
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: gpu: host1x: Fix use-after-free in host1x_bo_clear_cached_mappings [ Upstream
Commit: abeff53233b984571b87582bb588b4b38ef4ea50
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=abeff53233b984571b87582bb588b4b38ef4ea50
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68427
Analysis date: Mon, 10 Aug 2026 10:46:58 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-68427 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68427

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 7.0
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
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CVE-2026-68427	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-825;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free exists in host1x_bo_clear_cached_mappings() because __host1x_bo_unpin() can drop the last reference and free the mapping object before the function unlocks the cache mutex. The code then reads the cache pointer through the freed mapping object, which can trigger a kernel crash and is a real UAF condition in the GPU host1x buffer object cleanup path. For the CVSS the PR:L is used because a local user or process with access to the relevant GPU or host1x device interface may be able to trigger buffer object mapping cleanup without full administrator privileges. The issue is not network reachable and requires local interaction with the graphics device stack. Impact is at least local denial of service via kernel crash. In the paranoid interpretation, limited or full confidentiality and integrity impact cannot be excluded because stale object reuse around a freed kernel object may turn the UAF into a stronger memory corruption primitive, so this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	LOCK LEAK UAF HARDWARE  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local process with access to the relevant GPU or host1x device interface may be able to trigger BO mapping cleanup without full host root.
* Memory corruption, strong corruption primitive: +2. The commit explicitly describes a use-after-free after `__host1x_bo_unpin()` drops the last mapping reference.
* Real lifetime corruption: +1. This is a genuine stale pointer after free in object lifetime handling.
* Privileged kernel/device-management memory corruption path: +1. The bug is in GPU buffer mapping cache cleanup, a trusted kernel device-management path.
* Reliable kernel crash / strong DoS: +1. The freed object is dereferenced immediately after free and can plausibly crash under poisoning, debugging, or unlucky reuse.
* Corruption primitive highly constrained: -1. The demonstrated stale access is reading `mapping->cache` for `mutex_unlock()`, with no shown attacker-controlled reclaim, callback control, or arbitrary write.
* Rare / hardware-specific exposure: -1. The affected path is host1x/Tegra GPU specific, not a broad default subsystem on most Linux systems.
* Paranoid-only weak LPE concern: +1. If the freed mapping object is reclaimed before unlock, the stale cache pointer may become an unsafe object selection for mutex operations, but no controlled replacement primitive is shown.

3. Reachability analysis
A local attacker likely needs access to host1x/GPU device functionality that can create and clear cached buffer mappings. On systems exposing GPU device nodes to normal users, this is closer to PR:L. If the device is only accessible to root or a privileged graphics service, practical triggering is more restricted. Containers matter if the host GPU device is passed through or device cgroup policy exposes the relevant node. This is not network reachable. Exposure is hardware and driver dependent, mainly Tegra/host1x deployments.

Call-site confidence: high. The relevant call sequence is visible in the patch: lock cache, call `__host1x_bo_unpin()`, then dereference the potentially freed `mapping` object.

4. Severity interpretation
This is not an ordinary cleanup bug because the patch fixes an explicit kernel UAF. Realistically, the directly demonstrated impact is local DoS or debug-detected UAF rather than proven privilege escalation. The paranoid score is higher because stale kernel object reuse near a mutex operation deserves manual review, but the patch does not show attacker-controlled reclaim, arbitrary write, callback dispatch, or a reliable LPE chain. Overall this is Actionable Moderate, with Important-class escalation possible only if further analysis shows controllable reuse.

5. One-sentence report phrase
A local use-after-free in the host1x GPU buffer mapping cleanup path can occur when `__host1x_bo_unpin()` frees a mapping before `host1x_bo_clear_cached_mappings()` finishes using it, causing at least a kernel crash risk and requiring manual review for possible stale object reuse impact.

6. Manual review recommendation
MANUAL CHECK REQUIRED. Explicit kernel UAF in a device-facing path should not be auto-closed, even though the currently shown primitive is constrained and no reliable privilege escalation path is demonstrated.

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

Patch: gpu: host1x: Fix use-after-free in host1x_bo_clear_cached_mappings [ Upstream
Commit: abeff53233b984571b87582bb588b4b38ef4ea50
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=abeff53233b984571b87582bb588b4b38ef4ea50

Changed files:
  drivers/gpu/host1x/bus.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=abeff53233b984571b87582bb588b4b38ef4ea50

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

The original Linux kernel CVE announcement for CVE-2026-68427 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68427

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: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).