# CVE-2026-23177: mm, shmem: prevent infinite loop on truncate race

> A race condition in the Linux kernel's shmem truncation logic can cause an infinite loop, leading to a local denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 14 Feb 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2026-23177, DEBIAN-CVE-2026-23177, GHSA-xwq7-47qj-qwwf, ROOT-OS-DEBIAN-13-CVE-2026-23177, UBUNTU-CVE-2026-23177

## What is CVE-2026-23177?

CVE-2026-23177 is a denial of service vulnerability in Linux, published on 14 Feb 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, shmem: prevent infinite loop on truncate race

When truncating a large swap entry, shmem_free_swap() returns 0 when the
entry's index doesn't match the given index due to lookup alignment.  The
failure fallback path checks if the entry crosses the end border and
aborts when it happens, so truncate won't erase an unexpected entry or
range.  But one scenario was ignored.

When `index` points to the middle of a large swap entry, and the large
swap entry doesn't go across the end border, find_get_entries() will
return that large swap entry as the first item in the batch with
`indices[0]` equal to `index`.  The entry's base index will be smaller
than `indices[0]`, so shmem_free_swap() will fail and return 0 due to the
"base < index" check.  The code will then call shmem_confirm_swap(), get
the order, check if it crosses the END boundary (which it doesn't), and
retry with the same index.

The next iteration will find the same entry again at the same index with
same indices, leading to an infinite loop.

Fix this by retrying with a round-down index, and abort if the index is
smaller than the truncate range.

## Which versions are affected by CVE-2026-23177?


## How do I fix CVE-2026-23177?

Apply the vendor's patch.

## Is CVE-2026-23177 being exploited?

There is no known exploitation of CVE-2026-23177 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23177 and fix it if it is affected.

What it is: CVE-2026-23177 is a denial of service vulnerability in Linux, published on 14 Feb 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-2026-23177 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-2026-23177/ (Markdown: https://insights.sbomify.com/CVE-2026-23177/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23177
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23177
- OSV: https://osv.dev/vulnerability/CVE-2026-23177

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23177/
Summaries are generated and may contain mistakes; the official description above is the record.