# CVE-2026-53199: hv_netvsc: use kmap_local_page in netvsc_copy_to_send_buf

> A null dereference in the Hyper-V network driver causes a kernel crash when handling high memory pages on 32-bit systems with high memory enabled.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Jun 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-90767, BELL-CVE-2026-53199, DEBIAN-CVE-2026-53199, GHSA-69hj-phjm-g9c3, ROOT-OS-DEBIAN-11-CVE-2026-53199, ROOT-OS-DEBIAN-12-CVE-2026-53199, ROOT-OS-UBUNTU-2204-CVE-2026-53199, ROOT-OS-UBUNTU-2404-CVE-2026-53199, UBUNTU-CVE-2026-53199

## What is CVE-2026-53199?

CVE-2026-53199 is a high-severity vulnerability in Linux kernel, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

hv_netvsc: use kmap_local_page in netvsc_copy_to_send_buf

netvsc_copy_to_send_buf() copies page buffer entries into the VMBus
send buffer using phys_to_virt() on the entry PFN. Entries for the
RNDIS header and the skb linear data come from kmalloc'd memory and
are always in the kernel direct map, but entries for skb fragments
reference page cache or user pages, which on 32-bit x86 with
CONFIG_HIGHMEM=y can live above the LOWMEM boundary. For such a page
phys_to_virt() returns an address outside the direct map and the
subsequent memcpy() faults on the transmit softirq path, which is
fatal.

Map the pages with kmap_local_page() instead, handling two properties
of the page buffer entries:

 - pb[i].pfn is a Hyper-V PFN at HV_HYP_PAGE_SIZE (4K) granularity,
   not a native PFN. Reconstruct the physical address first and derive
   the native page from it, so the mapping stays correct where
   PAGE_SIZE > HV_HYP_PAGE_SIZE (e.g. arm64 with 64K pages).

 - Since commit 41a6328b2c55 ("hv_netvsc: Preserve contiguous PFN
   grouping in the page buffer array"), an entry describes a full
   physically contiguous fragment and pb[i].len can exceed PAGE_SIZE,
   while kmap_local_page() maps a single page. Copy page by page,
   splitting at native page boundaries.

The copy path only handles packets smaller than the send section size
(6144 bytes by default); larger packets take the cp_partial path where
only the RNDIS header is copied. So entries here are bounded by the
section size and a copy is split at most once on 4K-page systems. On
!CONFIG_HIGHMEM configs kmap_local_page() folds to page_address() and
no mapping work is added.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-53199?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53199?

Apply the vendor's patch.

## Is CVE-2026-53199 being exploited?

There is no known exploitation of CVE-2026-53199 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53199 and fix it if it is affected.

What it is: CVE-2026-53199 is a high-severity vulnerability in Linux kernel, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-53199 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-53199/ (Markdown: https://insights.sbomify.com/CVE-2026-53199/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53199
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53199
- OSV: https://osv.dev/vulnerability/CVE-2026-53199

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53199/
Summaries are generated and may contain mistakes; the official description above is the record.