* [CVE-2026-89818][MODERATE REGULAR] drm/amdgpu/vcn: fix integer overflow in dec_msg buffer count check
@ 2026-09-16 19:01 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-16 19:01 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89818
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu/vcn: fix integer overflow in dec_msg buffer count check
Commit: c2340281be4ddacb8c203e2bce59b126d1d6c4c8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c2340281be4ddacb8c203e2bce59b126d1d6c4c8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89818
Analysis date: Wed, 16 Sep 2026 15:01:47 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89818 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89818
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: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-89818 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89818 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H';CWE-190;CWE-125;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'An integer overflow in the AMDGPU VCN decoder message parser can allow a crafted num_buffers value to bypass the message length check. A value such as 0x3FFFFFFF makes the buffer count expression wrap to a small value, after which the parser can read far beyond the end of the message BO. Triggering also requires a mapping of about 4 GiB so that the crafted message length passes the earlier header bounds check, therefore AC:H is appropriate. For the CVSS the PR:L is selected because a local user or process with access to the DRM render node can submit crafted GPU command buffers without requiring full administrative privileges. The confirmed impact is an out of bounds read that can cause a kernel fault or crash and denial of service. The paranoid score also allows limited confidentiality impact because adjacent data may be read, but no integrity impact is assigned because no out of bounds write or arbitrary write primitive is established.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) SKIP CVE-2026-89818 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE OOB SIMPLEFIX HARDWARE TEST - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +1 Local unprivileged trigger. A process with access to the DRM render node can submit the crafted VCN message without host-admin-equivalent privilege.
* +1 Local unprivileged high-control kernel data-plane API. The submitter controls `num_buffers`, the message BO contents, and the approximately 4 GiB mapping required to pass the earlier check.
* +1 Reliable kernel crash or strong DoS. Successful bypass lets the kernel parser iterate far beyond the message BO, making a kernel fault or crash realistic.
* +0 Weak corruption concern. The established primitive is an OOB read caused by integer wraparound, not an OOB write or lifetime violation.
* No confidentiality point. No path returning OOB data to userspace, a device-visible output, or another observer is established.
* No integrity point. No subsequent write, controlled object mutation, or security-sensitive value influence is shown.
* No strong or weak LPE point. Controlled reclaim, arbitrary write, type confusion, callback influence, and privilege escalation are not demonstrated.
* No remote-reachability point. The vulnerable operation is local GPU command submission.
* No rare-hardware penalty. AMDGPU VCN is hardware-specific, but the supplied evidence does not establish rare or physical-only hardware.
* No timing penalty. The trigger requires a large mapping and crafted values, not a narrow or unreliable race.
Arithmetic: `1 + 1 + 1 = 3` for both conservative and paranoid scores.
3. Reachability analysis
An ordinary local process can reach the path if it has permission to open the AMDGPU render node and submit VCN decoder work. This is below host-admin privilege, although normal device-file access controls still apply.
The trigger requires affected AMDGPU VCN v3 or v4 hardware, a crafted decoder message, and an approximately 4 GiB mapping so that `msg[1]` passes the earlier header-size validation. No capability namespace governs the operation, and the complete trigger is not namespace-scoped. No race is involved, and attempts should be repeatable once the hardware, device access, and large mapping are available.
4. Primitive and severity interpretation
The exact primitive is an integer overflow in `6 + num_buffers * 4`, followed by an unbounded parser loop that performs OOB reads beyond the message BO. This is neither a UAF nor a repeated release or refcount mutation.
The demonstrated behavior is invalid read and probable kernel crash. The patch does not establish disclosure, write corruption, object replacement, or another useful primitive after excluding the crash. The approximately 4 GiB mapping raises practical trigger requirements but does not transform the issue into a race or host-admin-only path.
`CLASS_C` is appropriate because the supported consequence is primarily crash or DoS without an independently useful corruption primitive. `ImportantCandidate=NO` follows from the absence of write, disclosure, lifetime, or boundary-bypass leverage. `AutoDowngradeAllowed=YES` is appropriate, but manual review remains recommended to inspect the omitted parser loop for any downstream use of OOB values beyond ordinary reads.
5. One-sentence report phrase
A crafted AMDGPU VCN decoder message can overflow the buffer-count bounds calculation and make the kernel parser read far beyond a message BO, potentially causing a local kernel crash when a user with render-node access can create the required large mapping.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Review the omitted loop and its callees to confirm that OOB values cannot influence later object selection, writes, or user-visible output. The supplied patch itself establishes only OOB read and DoS.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: drm/amdgpu/vcn: fix integer overflow in dec_msg buffer count check
Commit: c2340281be4ddacb8c203e2bce59b126d1d6c4c8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c2340281be4ddacb8c203e2bce59b126d1d6c4c8
Commit description:
If the supplied msg[2] (num_buffers) is 0x3FFFFFFF, the expression
6 + num_buffers * 4 wraps to 2 and the bounds check passes, letting
the parser loop far past the end of the message BO. Triggering it
additionally requires a ~4GiB mapping so that msg[1] survives the
earlier "header does not fit in BO" check.
Rewrite the test in division form, which is overflow-free by
construction. Also update the message to reflect that msg is invalid.
Fixes: b193019 ("drm/amdgpu/vcn3: Prevent OOB reads when parsing dec msg")
Fixes: 0a78f2b ("drm/amdgpu/vcn4: Prevent OOB reads when parsing dec msg")
Cc: [email protected]
Signed-off-by: David (Ming Qiang) Wu <[email protected]>
Reviewed-by: Leo Liu <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/gpu/drm/amd/amdgpu/vcn_v3_0.c
drivers/gpu/drm/amd/amdgpu/vcn_v4_0.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=c2340281be4ddacb8c203e2bce59b126d1d6c4c8
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89818 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89818
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:L/I:N/A:H
The Best / paranoid CVSS score: 5.3
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: unknown
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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