# CVE-2025-21933: arm: pgtable: fix NULL pointer dereference issue

> A NULL pointer dereference in the Linux kernel ARM page table handling can cause a system crash during memory migration.

- **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:** 11 May 2026
- **Also known as:** BELL-CVE-2025-21933, GHSA-q5wj-cxq5-m47h, UBUNTU-CVE-2025-21933

## What is CVE-2025-21933?

CVE-2025-21933 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:

arm: pgtable: fix NULL pointer dereference issue

When update_mmu_cache_range() is called by update_mmu_cache(), the vmf
parameter is NULL, which will cause a NULL pointer dereference issue in
adjust_pte():

Unable to handle kernel NULL pointer dereference at virtual address 00000030 when read
Hardware name: Atmel AT91SAM9
PC is at update_mmu_cache_range+0x1e0/0x278
LR is at pte_offset_map_rw_nolock+0x18/0x2c
Call trace:
 update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec
 remove_migration_pte from rmap_walk_file+0xcc/0x130
 rmap_walk_file from remove_migration_ptes+0x90/0xa4
 remove_migration_ptes from migrate_pages_batch+0x6d4/0x858
 migrate_pages_batch from migrate_pages+0x188/0x488
 migrate_pages from compact_zone+0x56c/0x954
 compact_zone from compact_node+0x90/0xf0
 compact_node from kcompactd+0x1d4/0x204
 kcompactd from kthread+0x120/0x12c
 kthread from ret_from_fork+0x14/0x38
Exception stack(0xc0d8bfb0 to 0xc0d8bff8)

To fix it, do not rely on whether 'ptl' is equal to decide whether to hold
the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is
enabled.  In addition, if two vmas map to the same PTE page, there is no
need to hold the pte lock again, otherwise a deadlock will occur.  Just
add the need_lock parameter to let adjust_pte() know this information.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2025-21933?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21933?

Apply the vendor's patch.

## Is CVE-2025-21933 being exploited?

There is no known exploitation of CVE-2025-21933 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-2025-21933 and fix it if it is affected.

What it is: CVE-2025-21933 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-2025-21933 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-2025-21933/ (Markdown: https://insights.sbomify.com/CVE-2025-21933/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21933
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21933
- OSV: https://osv.dev/vulnerability/CVE-2025-21933

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21933/
Summaries are generated and may contain mistakes; the official description above is the record.