# CVE-2026-72173: fs/proc/task_mmu: do not warn on seeing non-migration pmd entry

> A stale kernel warning in the proc filesystem can be triggered by local users, potentially causing log spam or system instability.

- **Severity:** Not scored
- **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:** 15 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-72173, GHSA-hw29-pcpv-9423, UBUNTU-CVE-2026-72173

## What is CVE-2026-72173?

CVE-2026-72173 is a denial of service vulnerability in Linux, published on 15 Aug 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:

fs/proc/task_mmu: do not warn on seeing non-migration pmd entry

Patch series "mm/hmm: A fix and a selftest", v3.

Patch 1 fixes a stale warning present from the time when only migration
softleaf entries were supported at the PMD level.

Patch 2 adds some code into hmm-tests.c which exercises the pagemap path
for PMD device-private entries.

This patch (of 2):

pagemap_pmd_range_thp() warns if a non-present PMD is not a migration
entry.  This became false once device-private entries at the PMD level
were added.

Therefore, remove the stale migration-only assertion.

## Which versions are affected by CVE-2026-72173?


## How do I fix CVE-2026-72173?

Apply the vendor's patch.

## Is CVE-2026-72173 being exploited?

There is no known exploitation of CVE-2026-72173 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72173 and fix it if it is affected.

What it is: CVE-2026-72173 is a denial of service vulnerability in Linux, published on 15 Aug 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-2026-72173 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-2026-72173/ (Markdown: https://insights.sbomify.com/CVE-2026-72173/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72173
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72173
- OSV: https://osv.dev/vulnerability/CVE-2026-72173

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72173/
Summaries are generated and may contain mistakes; the official description above is the record.