* [CVE-2026-80887][IMPORTANT] drm/vmwgfx: use check_add_overflow for shader size+offset bound
@ 2026-09-04 20:28 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-04 20:28 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80887
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: drm/vmwgfx: use check_add_overflow for shader size+offset bound
Commit: 1bbe7751f5ebac383405ef29a66622d65bd505d3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1bbe7751f5ebac383405ef29a66622d65bd505d3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80887
Analysis date: Fri, 04 Sep 2026 16:28:47 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES
Summary:
A vmwgfx shader bounds check can be bypassed by overflowing the user supplied shader size plus offset, allowing an invalid guest_memory_offset to be forwarded to SVGA shader creation. For the CVSS the PR:L is used because triggering requires local access to the vmwgfx DRM device. The issue is not network reachable, but the virtual GPU boundary makes host side impact plausible enough for manual review.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80887 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80887
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
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CVE-2026-80887 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-80887 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:C/C:H/I:H/A:H';CWE-190;*CWE-20;CWE-1284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '8.8';DESCR 'A bounds check in vmw_shader_define can be bypassed because the user supplied shader size plus offset can wrap when offset is near U64_MAX. The wrapped endpoint may pass validation even though the real shader window is outside the backing buffer, and the unchecked offset is then stored as guest_memory_offset and sent to host SVGA shader create commands. For the CVSS the PR:L is used because a local user with access to the vmwgfx DRM device or render node can supply the shader parameters through the driver interface. The issue is not network reachable and requires local execution in the guest or on the affected system. Impact is at least a local integrity and availability risk through invalid buffer range handling, and the virtual GPU boundary makes host side impact plausible enough for manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES SIMPLEFIX HARDWARE LINUS KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS8.5PLUS NO NO checked
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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=5
## 1. ActionableScore
* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::
## 2. Signal breakdown
Conservative signals:
* Local unprivileged trigger: +1. A local user with access to the vmwgfx DRM device or render node can supply shader size and offset through the ioctl path.
* Strong attacker-influenced semantic reinterpretation primitive: +2. The shader window is validated using a wrapped size plus offset endpoint, but the original unbounded offset is later stored as guest_memory_offset and consumed by the SVGA shader-create command path.
* Weak or indirect corruption candidate: +1. The patch does not prove an arbitrary write or UAF, but it does show an out-of-range offset crossing into a trusted GPU command interface.
* Integrity impact plausible: +1. The invalid shader memory range may affect object/resource interpretation or shader data ownership.
* Configuration-specific exposure: -1. This is vmwgfx-specific and mainly relevant to VMware virtual GPU environments.
Paranoid additional signals:
* Weak LPE or boundary-crossing concern: +1. The bug crosses the guest driver to host SVGA command boundary, so guest-to-host or host-backend impact is plausible enough for manual review.
* Confidentiality impact plausible: +1. A malformed offset into guest memory metadata could plausibly cause unintended memory/resource access in the backend, though this is not proven by the patch.
* Cross-boundary isolation or policy bypass concern: +1. The affected path is a virtualization graphics interface where a guest-controlled descriptor is forwarded to host-side device emulation.
## 3. Reachability analysis
The bug is locally reachable through the vmwgfx DRM shader creation path, assuming the attacker can access the relevant DRM device node inside the guest or affected system. For the CVSS the PR:L interpretation is appropriate because a local user context is required, but full root or CAP_SYS_ADMIN is not necessarily required if render or DRM access is delegated. The path is not network reachable. Containers and sandboxes matter if they expose the vmwgfx device node, because reduced-capability root or a service account with device access should not be treated as full host-root. The main practical precondition is use of the VMware virtual GPU stack.
Call-site confidence: medium. The patch shows the validation point and the downstream storage into guest_memory_offset, but the exact host SVGA backend behavior is not included.
## 4. Severity interpretation
This is stronger than an ordinary Moderate validation bug because the failed bounds check allows a user-controlled U64 offset near U64_MAX to survive validation and reach a virtualization device command path. The conservative interpretation is Actionable Moderate because the patch supports an out-of-range offset primitive but does not prove arbitrary memory corruption, controlled overwrite, or a working privilege escalation chain. The paranoid interpretation is Strong Important candidate because virtual GPU command descriptors cross a guest-to-host trust boundary, and manual analysis of the host SVGA backend is needed to rule out host-side memory corruption or guest-to-host impact.
## 5. One-sentence report phrase
A vmwgfx shader bounds check can be bypassed by overflowing the user supplied shader size plus offset, allowing an invalid guest_memory_offset to be forwarded to SVGA shader creation. For the CVSS the PR:L is used because triggering requires local access to the vmwgfx DRM device. The issue is not network reachable, but the virtual GPU boundary makes host side impact plausible enough for manual review.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.
Reason: the patch demonstrates a concrete integer-overflow bounds bypass with an unchecked offset forwarded into a virtualization GPU command path. Even though arbitrary code execution is not demonstrated, the guest-to-host boundary and pointer/offset-bearing command semantics make auto-close unsafe.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: drm/vmwgfx: use check_add_overflow for shader size+offset bound
Commit: 1bbe7751f5ebac383405ef29a66622d65bd505d3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1bbe7751f5ebac383405ef29a66622d65bd505d3
Commit description:
vmw_shader_define() validates the user-supplied shader window against
its backing buffer with
(u64)buffer->tbo.base.size < (u64)size + (u64)offset
drm_vmw_shader_create_arg::offset is __u64 in the uapi; when it is
near U64_MAX the unsigned addition wraps and the resulting tiny value
passes the check. The unbounded offset is then stored in
res->guest_memory_offset and forwarded to host SVGA shader-create
commands.
Use check_add_overflow() to detect the wrap and compare the resulting
endpoint against the buffer size.
Fixes: 668b206 ("drm/vmwgfx: Stop using raw ttm_buffer_object's")
Cc: [email protected]
Assisted-by: Claude:claude-opus-4.7
Signed-off-by: Zack Rusin <[email protected]>
Reviewed-by: Ian Forbes <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/gpu/drm/vmwgfx/vmwgfx_shader.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=1bbe7751f5ebac383405ef29a66622d65bd505d3
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DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80887 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80887
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:L/PR:L/UI:N/S:U/C:L/I:L/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
The Best / paranoid CVSS score: 8.8
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: 5
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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