# CVE-2026-89755: mm/migrate_device: clear stale mapping after freeing swapcache

> A use-after-free vulnerability in the Linux kernel's device migration code can cause a reference count bug and system crash.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 11 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-100413, BELL-CVE-2026-89755, DEBIAN-CVE-2026-89755, GHSA-f448-r8g9-p8j7, UBUNTU-CVE-2026-89755

## What is CVE-2026-89755?

CVE-2026-89755 is a high-severity use after free vulnerability in Linux, published on 11 Sep 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:

mm/migrate_device: clear stale mapping after freeing swapcache

__migrate_device_pages() reads the folio mapping before calling
folio_free_swap().  When folio_free_swap() succeeds, the folio is removed
from the swap cache, but the saved mapping still points to swap_space.

Passing the stale mapping to folio_migrate_mapping() makes it use the
mapped-folio path for a folio that is no longer in swapcache.  It can then
operate on swap_space.i_pages with invalid reference accounting,
eventually triggering a folio reference count BUG.

After a successful split, nr still contains the number of pages in the
original large folio, although each resulting page is now a separate
order-0 folio.  Reset nr to 1 so each split folio is processed separately,
including its own swapcache removal and mapping lookup.

Refresh the saved mapping after folio_free_swap() so the current folio
state is used during migration.

## Which versions are affected by CVE-2026-89755?


## How do I fix CVE-2026-89755?

Apply the vendor's patch.

## Is CVE-2026-89755 being exploited?

There is no known exploitation of CVE-2026-89755 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89755 and fix it if it is affected.

What it is: CVE-2026-89755 is a high-severity use after free vulnerability in Linux, published on 11 Sep 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-2026-89755 in the wild and no public exploit code.

Affected product: Linux. 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-2026-89755/ (Markdown: https://insights.sbomify.com/CVE-2026-89755/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89755
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89755
- OSV: https://osv.dev/vulnerability/CVE-2026-89755

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89755/
Summaries are generated and may contain mistakes; the official description above is the record.