# CVE-2026-43073: x86-64: rename misleadingly named '__copy_user_nocache()' function

> The Linux kernel renamed a misleadingly named memory copy function to improve code clarity and prevent misuse by drivers, with no direct security impact stated.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 5 May 2026
- **Updated:** 21 Oct 2026
- **Also known as:** BELL-CVE-2026-43073, DEBIAN-CVE-2026-43073, GHSA-w93x-73ch-q28m, ROOT-OS-DEBIAN-11-CVE-2026-43073, ROOT-OS-DEBIAN-12-CVE-2026-43073, ROOT-OS-UBUNTU-2204-CVE-2026-43073, ROOT-OS-UBUNTU-2404-CVE-2026-43073, UBUNTU-CVE-2026-43073

## What is CVE-2026-43073?

CVE-2026-43073 is a medium-severity vulnerability in Linux kernel, published on 5 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

x86-64: rename misleadingly named '__copy_user_nocache()' function

This function was a masterclass in bad naming, for various historical
reasons.

It claimed to be a non-cached user copy.  It is literally _neither_ of
those things.  It's a specialty memory copy routine that uses
non-temporal stores for the destination (but not the source), and that
does exception handling for both source and destination accesses.

Also note that while it works for unaligned targets, any unaligned parts
(whether at beginning or end) will not use non-temporal stores, since
only words and quadwords can be non-temporal on x86.

The exception handling means that it _can_ be used for user space
accesses, but not on its own - it needs all the normal "start user space
access" logic around it.

But typically the user space access would be the source, not the
non-temporal destination.  That was the original intention of this,
where the destination was some fragile persistent memory target that
needed non-temporal stores in order to catch machine check exceptions
synchronously and deal with them gracefully.

Thus that non-descriptive name: one use case was to copy from user space
into a non-cached kernel buffer.  However, the existing users are a mix
of that intended use-case, and a couple of random drivers that just did
this as a performance tweak.

Some of those random drivers then actively misused the user copying
version (with STAC/CLAC and all) to do kernel copies without ever even
caring about the exception handling, _just_ for the non-temporal
destination.

Rename it as a first small step to actually make it halfway sane, and
change the prototype to be more normal: it doesn't take a user pointer
unless the caller has done the proper conversion, and the argument size
is the full size_t (it still won't actually copy more than 4GB in one
go, but there's also no reason to silently truncate the size argument in
the caller).

Finally, use this now sanely named function in the NTB code, which
mis-used a user copy version (with STAC/CLAC and all) of this interface
despite it not actually being a user copy at all.

## Which versions are affected by CVE-2026-43073?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43073?

Apply the vendor's patch.

## Is CVE-2026-43073 being exploited?

There is no known exploitation of CVE-2026-43073 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-2026-43073 and fix it if it is affected.

What it is: CVE-2026-43073 is a medium-severity vulnerability in Linux kernel, published on 5 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-43073 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-2026-43073/ (Markdown: https://insights.sbomify.com/CVE-2026-43073/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43073
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43073
- OSV: https://osv.dev/vulnerability/CVE-2026-43073

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43073/
Summaries are generated and may contain mistakes; the official description above is the record.