# CVE-2025-37818: LoongArch: Return NULL from huge_pte_offset() for invalid PMD

> A local attacker can cause a kernel crash on LoongArch systems by triggering a null pointer dereference in the huge page table handling code.

- **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:** 8 May 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-37818, DEBIAN-CVE-2025-37818, GHSA-4q4q-jv3m-fqjr, ROOT-OS-DEBIAN-12-CVE-2025-37818, ROOT-OS-UBUNTU-2204-CVE-2025-37818, UBUNTU-CVE-2025-37818

## What is CVE-2025-37818?

CVE-2025-37818 is a medium-severity vulnerability in Debian Debian Linux, published on 8 May 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:

LoongArch: Return NULL from huge_pte_offset() for invalid PMD

LoongArch's huge_pte_offset() currently returns a pointer to a PMD slot
even if the underlying entry points to invalid_pte_table (indicating no
mapping). Callers like smaps_hugetlb_range() fetch this invalid entry
value (the address of invalid_pte_table) via this pointer.

The generic is_swap_pte() check then incorrectly identifies this address
as a swap entry on LoongArch, because it satisfies the "!pte_present()
&& !pte_none()" conditions. This misinterpretation, combined with a
coincidental match by is_migration_entry() on the address bits, leads to
kernel crashes in pfn_swap_entry_to_page().

Fix this at the architecture level by modifying huge_pte_offset() to
check the PMD entry's content using pmd_none() before returning. If the
entry is invalid (i.e., it points to invalid_pte_table), return NULL
instead of the pointer to the slot.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2025-37818?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-37818?

Apply the vendor's patch.

## Is CVE-2025-37818 being exploited?

There is no known exploitation of CVE-2025-37818 in the wild and no public exploit code.

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## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-37818 and fix it if it is affected.

What it is: CVE-2025-37818 is a medium-severity vulnerability in Debian Debian Linux, published on 8 May 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-2025-37818 in the wild and no public exploit code.

Affected product: Debian Debian 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-2025-37818/ (Markdown: https://insights.sbomify.com/CVE-2025-37818/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-37818
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-37818
- OSV: https://osv.dev/vulnerability/CVE-2025-37818

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-37818/
Summaries are generated and may contain mistakes; the official description above is the record.