# CVE-2026-98866: sched/cache: Introduce task_struct->sched_cache_grp to fix UAF

> A use-after-free in the Linux kernel scheduler allows local attackers to execute arbitrary code or escalate privileges.

- **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:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-98866, GHSA-3r69-998r-q4c2, UBUNTU-CVE-2026-98866

## What is CVE-2026-98866?

CVE-2026-98866 is an use after free vulnerability in Linux, published on 18 Oct 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:

sched/cache: Introduce task_struct->sched_cache_grp to fix UAF

Add a sched_cache_grp pointer to task_struct so that scheduler code
can access the cache group directly via the task, without going
through mm->sched_cache_grp.  This decouples the scheduler's hot-path
accesses from the mm_struct.

Each task holds its own refcount on the sched_cache_group, separate
from the reference held by its mm_struct.  The reference is acquired
in copy_mm() (fork) and exec_mmap() (exec), and released in exit_mm().
This fixes the use-after-free when account_mm_sched() reaches the group
through a task whose mm is being switched, as reported by Hyunwoo:

  https://lore.kernel.org/lkml/apPb-Dr4nPYuHQOK@v4bel/

Convert all scheduler code in fair.c and exit.c to use
p->sched_cache_grp instead of p->mm->sched_cache_grp.

Keep the fork/exec/exit reference management out of the generic mm
paths: add sched_cache_fork(), sched_cache_fork_cleanup(),
sched_cache_exec_mmap() and sched_cache_exit_mm() in
kernel/sched/cache_sched.c (with empty stubs for !CONFIG_SCHED_CACHE),
so fs/exec.c, kernel/fork.c and kernel/exit.c each call one helper
instead of open-coding the refcounting under #ifdef.  Also add
sched_cache_group_get() and task_cache_group_get().

## Which versions are affected by CVE-2026-98866?


## How do I fix CVE-2026-98866?

Apply the vendor's patch.

## Is CVE-2026-98866 being exploited?

There is no known exploitation of CVE-2026-98866 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98866 and fix it if it is affected.

What it is: CVE-2026-98866 is an use after free vulnerability in Linux, published on 18 Oct 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-2026-98866 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-2026-98866/ (Markdown: https://insights.sbomify.com/CVE-2026-98866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98866
- OSV: https://osv.dev/vulnerability/CVE-2026-98866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98866/
Summaries are generated and may contain mistakes; the official description above is the record.