# CVE-2025-21931: hwpoison, memory_hotplug: lock folio before unmap hwpoisoned folio

> A missing folio lock in the Linux kernel memory hotplug path causes a kernel bug and system crash when offlining hardware-poisoned pages.

- **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:** 1 Apr 2025
- **Updated:** 23 May 2026
- **Also known as:** BELL-CVE-2025-21931, DEBIAN-CVE-2025-21931, GHSA-g2g9-6hgr-7f52, ROOT-OS-DEBIAN-11-CVE-2025-21931, ROOT-OS-DEBIAN-12-CVE-2025-21931, ROOT-OS-UBUNTU-2204-CVE-2025-21931, ROOT-OS-UBUNTU-2404-CVE-2025-21931, UBUNTU-CVE-2025-21931

## What is CVE-2025-21931?

CVE-2025-21931 is a medium-severity vulnerability in Linux kernel, published on 1 Apr 2025. 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:

hwpoison, memory_hotplug: lock folio before unmap hwpoisoned folio

Commit b15c87263a69 ("hwpoison, memory_hotplug: allow hwpoisoned pages to
be offlined) add page poison checks in do_migrate_range in order to make
offline hwpoisoned page possible by introducing isolate_lru_page and
try_to_unmap for hwpoisoned page.  However folio lock must be held before
calling try_to_unmap.  Add it to fix this problem.

Warning will be produced if folio is not locked during unmap:

  ------------[ cut here ]------------
  kernel BUG at ./include/linux/swapops.h:400!
  Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
  Modules linked in:
  CPU: 4 UID: 0 PID: 411 Comm: bash Tainted: G        W          6.13.0-rc1-00016-g3c434c7ee82a-dirty #41
  Tainted: [W]=WARN
  Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
  pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  pc : try_to_unmap_one+0xb08/0xd3c
  lr : try_to_unmap_one+0x3dc/0xd3c
  Call trace:
   try_to_unmap_one+0xb08/0xd3c (P)
   try_to_unmap_one+0x3dc/0xd3c (L)
   rmap_walk_anon+0xdc/0x1f8
   rmap_walk+0x3c/0x58
   try_to_unmap+0x88/0x90
   unmap_poisoned_folio+0x30/0xa8
   do_migrate_range+0x4a0/0x568
   offline_pages+0x5a4/0x670
   memory_block_action+0x17c/0x374
   memory_subsys_offline+0x3c/0x78
   device_offline+0xa4/0xd0
   state_store+0x8c/0xf0
   dev_attr_store+0x18/0x2c
   sysfs_kf_write+0x44/0x54
   kernfs_fop_write_iter+0x118/0x1a8
   vfs_write+0x3a8/0x4bc
   ksys_write+0x6c/0xf8
   __arm64_sys_write+0x1c/0x28
   invoke_syscall+0x44/0x100
   el0_svc_common.constprop.0+0x40/0xe0
   do_el0_svc+0x1c/0x28
   el0_svc+0x30/0xd0
   el0t_64_sync_handler+0xc8/0xcc
   el0t_64_sync+0x198/0x19c
  Code: f9407be0 b5fff320 d4210000 17ffff97 (d4210000)
  ---[ end trace 0000000000000000 ]---

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2025-21931?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21931?

Apply the vendor's patch.

## Is CVE-2025-21931 being exploited?

There is no known exploitation of CVE-2025-21931 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-2025-21931 and fix it if it is affected.

What it is: CVE-2025-21931 is a medium-severity vulnerability in Linux kernel, published on 1 Apr 2025. 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-2025-21931 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-2025-21931/ (Markdown: https://insights.sbomify.com/CVE-2025-21931/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21931
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21931
- OSV: https://osv.dev/vulnerability/CVE-2025-21931

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21931/
Summaries are generated and may contain mistakes; the official description above is the record.