# CVE-2026-93197: memcg: move LRU size accounting on reparenting instead of copying it

> A Linux kernel bug causes stale LRU accounting in offlined memory cgroups, leading to excessive CPU consumption and potential denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-93197, GHSA-36hf-5688-v4hm, UBUNTU-CVE-2026-93197

## What is CVE-2026-93197?

CVE-2026-93197 is a denial of service vulnerability in Linux, published on 17 Sep 2026. 

### Official description

In the Linux kernel, the following vulnerability has been resolved:

memcg: move LRU size accounting on reparenting instead of copying it

When a memory cgroup is offlined its LRU folios are reparented to the
parent.  lruvec_reparent_lru() splices the child's lists into the
parent's and credits the parent with the child's per-zone
lru_zone_size[], but never clears the child's copy, so the size is
copied rather than moved.  lru_gen_reparent_memcg() does the same for
MGLRU.

The parent is left correct, credited with exactly the folios it took
over.  The stale value sits on the child and nothing will correct it:
folio->memcg_data now resolves to the parent, so every later
update_lru_size() for those folios goes there.

Dying cgroups are not freed immediately and mem_cgroup_iter() still
walks them, so shrink_lruvec() keeps being called on them.
get_scan_count() reads the phantom counter through lruvec_lru_size() and
the scan loop then grinds through nr[] in SWAP_CLUSTER_MAX steps against
an empty list, for as long as the dead cgroup lives.  Under MGLRU the
MGLRU scanner runs instead, but count_shadow_nodes() sums all of
NR_LRU_LISTS through lruvec_lru_size() and over-budgets the shadow node
limit just the same.

On one 251 GiB host a sweep of every mz->lru_zone_size[] found 380
counters describing folios on no list at all: 124777314 pages, 476 GiB,
1.89x the machine's RAM, across 57 cgroups.  All were on memcgs with
CSS_DYING set and CSS_ONLINE clear, and parent/child pairs reported
byte-identical sizes.

LRU_UNEVICTABLE needs its size moved too.  Its list is deliberately not
spliced because lruvec_init() poisons the head - the unevictable LRU is
imaginary and folios are never threaded on it - but the size is kept by
lruvec_add_folio()/lruvec_del_folio() and those folios account to the
parent from here on.

This depends on commit bf4ade7dbd76 ("memcg: keep folio's objcg same as
its node") and must not be backported ahead of it.  Without that
invariant a folio's objcg can belong to another node, so a folio already
spliced onto the parent's list can still resolve to the child's lruvec
until the objcg's node is reparented in a later iteration of
memcg_reparent_objcgs(); clearing the child's counter early then lets
lruvec_del_folio() underflow it and trip the WARN_ONCE()/VM_BUG_ON() in
mem_cgroup_update_lru_size().

## Which versions are affected by CVE-2026-93197?


## How do I fix CVE-2026-93197?

Apply the vendor's patch.

## Is CVE-2026-93197 being exploited?

There is no known exploitation of CVE-2026-93197 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93197 and fix it if it is affected.

What it is: CVE-2026-93197 is a denial of service vulnerability in Linux, published on 17 Sep 2026. 
Exploitation: There is no known exploitation of CVE-2026-93197 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-2026-93197/ (Markdown: https://insights.sbomify.com/CVE-2026-93197/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93197
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93197
- OSV: https://osv.dev/vulnerability/CVE-2026-93197

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93197/
Summaries are generated and may contain mistakes; the official description above is the record.