# CVE-2026-89985: memcg: keep folio's objcg same as its node

> A race condition in Linux kernel memory cgroup reparenting can cause lock mismatches, potentially leading to system crashes or denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-89985, GHSA-5r45-xw38-xrg8, UBUNTU-CVE-2026-89985

## What is CVE-2026-89985?

CVE-2026-89985 is a high-severity 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:

memcg: keep folio's objcg same as its node

memcg_reparent_objcgs() has an inherent assumption that a folio's objcg is
the objcg of the folio's node.  Folio migration across nodes breaks that
assumption: the new folio simply inherits the old folio's objcg while
living on a different node.

Once the assumption is broken, the reparenting of the folio's objcg and
the reparenting of the folio's LRU list are no longer atomic. 
memcg_reparent_objcgs() handles one node per iteration and drops all the
locks in between, so the objcg gets reparented in the iteration for the
objcg's node while the LRU list gets spliced in the iteration for the
folio's node.  Any LRU operation on that folio in between resolves its
lruvec through the objcg, and thus takes the lru_lock of the wrong memcg,
not the lru_lock of the list the folio is actually on.

Fix this by selecting the objcg by folio_nid() at charge time, and by
re-deriving it for the destination node in mem_cgroup_migrate() and
mem_cgroup_replace_folio().

## Which versions are affected by CVE-2026-89985?


## How do I fix CVE-2026-89985?

Apply the vendor's patch.

## Is CVE-2026-89985 being exploited?

There is no known exploitation of CVE-2026-89985 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89985 and fix it if it is affected.

What it is: CVE-2026-89985 is a high-severity 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-2026-89985 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-2026-89985/ (Markdown: https://insights.sbomify.com/CVE-2026-89985/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89985
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89985
- OSV: https://osv.dev/vulnerability/CVE-2026-89985

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89985/
Summaries are generated and may contain mistakes; the official description above is the record.