[CVE-2026-53199][MODERATE REGULAR] hv_netvsc: use kmap_local_page in netvsc_copy_to_send_buf [ Upstream

[CVE-2026-53199][MODERATE REGULAR] hv_netvsc: use kmap_local_page in netvsc_copy_to_send_buf [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53199
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: hv_netvsc: use kmap_local_page in netvsc_copy_to_send_buf [ Upstream
Commit: 16514afeb7d3d121072ba9a0b640d6c1c5507db0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=16514afeb7d3d121072ba9a0b640d6c1c5507db0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53199
Analysis date: Thu, 25 Jun 2026 06:02:46 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
hv_netvsc can crash a Hyper-V guest on transmit when skb fragments reference highmem pages and netvsc_copy_to_send_buf uses phys_to_virt instead of mapping the page correctly.

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

The original Linux kernel CVE announcement for CVE-2026-53199 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53199

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-2026-53199	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-754;CWE-703;CWE-119;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.9';DESCR 'hv_netvsc can crash on transmit because netvsc_copy_to_send_buf used phys_to_virt on page buffer PFNs from skb fragments. On 32 bit x86 with CONFIG_HIGHMEM, these fragments can point to high memory pages that are not in the direct map, so memcpy can fault in the transmit softirq path and cause a fatal kernel crash. Reliable triggering normally requires a local user or process that can make the guest transmit packets using skb fragments from page cache or user pages, with packet size below the send section copy threshold. For the CVSS the PR:N is used for the paranoid score because a remote client may be able to induce an exposed service to transmit such fragmented data, but this is environment dependent and higher complexity. The issue is not a proven memory corruption primitive and impact is denial of service via guest kernel crash.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	OOB NETWORK SKB MEMORY PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

Conservative scoring:

* Local unprivileged trigger: +1. A local unprivileged process may be able to make the guest transmit skb fragments backed by page cache or user pages.
* Reliable kernel crash / strong DoS: +1. The commit explicitly says memcpy can fault in TX softirq context and this is fatal.
* Availability impact realistic: +1. In the affected configuration this can crash the guest kernel, not just fail one packet.
* Rare AND difficult-to-reach subsystem/configuration: -1. Requires Hyper-V netvsc plus 32-bit x86 with CONFIG_HIGHMEM and skb fragments in the sendbuf copy path.

Paranoid scoring:

* Remote reachable / network-triggerable: +2. Not a direct remote packet parsing bug, but a remote client may be able to induce an exposed service in the guest to transmit file-backed or user-page-backed fragments over hv_netvsc.
* Reliable kernel crash / strong DoS: +1.
* Availability impact realistic: +1.
* Rare AND difficult-to-reach subsystem/configuration: -1.

Not counted:

* No generic memory corruption bonus. The patch shows an invalid direct-map assumption and a faulting memcpy source address, not UAF, OOB write, double-free, type confusion, or attacker-controlled overwrite.
* No privilege escalation bonus. There is no supported reclaim, write primitive, callback corruption, or object confusion.
* No confidentiality or integrity impact. The demonstrated effect is crash-only.

## 3. Reachability analysis

The conservative trigger is local inside a Hyper-V guest. A local user or process must cause transmit traffic using skb fragments that reference highmem page cache or user pages, and the packet must use the sendbuf copy path rather than the larger cp_partial path.

The paranoid trigger is network-assisted. A remote client could potentially request data from a service running in the guest and cause that service to transmit affected fragmented skbs. This requires a suitable exposed service and the rare affected guest configuration, so it should not be treated like a normal remotely reachable protocol parser bug.

Namespaces do not materially change the core issue. If an unprivileged container or namespace can cause the guest to transmit affected fragmented traffic, it may be enough for DoS, but the crash affects the guest kernel.

## 4. Severity interpretation

This behaves like a targeted DoS issue, not an Important-class memory corruption vulnerability. The theoretical concern is that memcpy uses an invalid virtual address derived from a highmem page PFN, but the patch does not support attacker-controlled memory corruption or privilege escalation.

The conservative result is Low-like to ordinary Moderate. The paranoid result is borderline because network-assisted triggering may be possible through exposed services, but the affected setup is narrow.

## 5. One-sentence report phrase

hv_netvsc can crash a Hyper-V guest on transmit when skb fragments reference highmem pages and netvsc_copy_to_send_buf uses phys_to_virt instead of mapping the page correctly.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a network driver TX path and a network-assisted DoS may be possible through exposed services, but the issue is limited to rare 32-bit HIGHMEM guest configurations and does not show a memory corruption or privilege escalation primitive.

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

Patch: hv_netvsc: use kmap_local_page in netvsc_copy_to_send_buf [ Upstream
Commit: 16514afeb7d3d121072ba9a0b640d6c1c5507db0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=16514afeb7d3d121072ba9a0b640d6c1c5507db0

Changed files:
  drivers/net/hyperv/netvsc.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=16514afeb7d3d121072ba9a0b640d6c1c5507db0

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

The original Linux kernel CVE announcement for CVE-2026-53199 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53199

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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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).