# CVE-2026-89834: f2fs: fix to migrate all curseg types during free_segment_range

> A local attacker with high privileges can trigger out-of-bounds I/O during filesystem shrink, potentially causing denial of service or code execution.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-101523, BELL-CVE-2026-89834, DEBIAN-CVE-2026-89834, GHSA-92fw-gww6-96g8, UBUNTU-CVE-2026-89834

## What is CVE-2026-89834?

CVE-2026-89834 is a memory corruption vulnerability in Linux, published on 16 Sep 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:

f2fs: fix to migrate all curseg types during free_segment_range

In free_segment_range(), the curseg evacuation loop only iterates up to
NR_CURSEG_PERSIST_TYPE (0..5), missing non-persistent in-memory curseg
types such as CURSEG_COLD_DATA_PINNED and CURSEG_ALL_DATA_ATGC.

Even though these in-memory curseg types are not saved in the on-disk
checkpoint header, they still occupy active physical segments at runtime.
If an active in-memory curseg happens to be allocated within the segment
range being truncated during filesystem shrink, failing to evacuate it
will cause subsequent writes to the curseg attempting out-of-bounds I/O
on the truncated storage range.

Fix this by expanding the curseg evacuation loop upper bound to
NR_CURSEG_TYPE to ensure all active curseg types are safely migrated
out of the target range.

## Which versions are affected by CVE-2026-89834?


## How do I fix CVE-2026-89834?

Apply the vendor's patch.

## Is CVE-2026-89834 being exploited?

There is no known exploitation of CVE-2026-89834 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89834 and fix it if it is affected.

What it is: CVE-2026-89834 is a memory corruption vulnerability in Linux, published on 16 Sep 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-2026-89834 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-2026-89834/ (Markdown: https://insights.sbomify.com/CVE-2026-89834/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89834
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89834
- OSV: https://osv.dev/vulnerability/CVE-2026-89834

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89834/
Summaries are generated and may contain mistakes; the official description above is the record.