# CVE-2026-98788: futex: Fix private hash use-after-free on resize

> A use-after-free vulnerability in the Linux kernel futex subsystem allows local attackers to potentially execute 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:** BELL-CVE-2026-98788, DEBIAN-CVE-2026-98788, GHSA-qwmc-gmgx-xf8h, UBUNTU-CVE-2026-98788

## What is CVE-2026-98788?

CVE-2026-98788 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:

futex: Fix private hash use-after-free on resize

poll_state_synchronize_rcu(mm->futex.phash.batches) is used by
futex_ref_drop() to check that a grace period has passed since the
current hash was published. This relies on batches referencing a grace
period which started after the hash pointer was assigned.

__futex_pivot_hash() sets mmph->batches before it replaces mmph->hash:

    scoped_guard(rcu) {
            mmph->batches = get_state_synchronize_rcu();
            rcu_assign_pointer(mmph->hash, new);
    }

The scoped_guard(rcu) doesn't stop new grace periods from starting, and
if one starts between those two assignments, futex_ref_drop() can move
forward while a reader still holds a pointer to the old hash.

Fix things by setting mmph->batches after assigning mmph->hash.  The
scoped_guard(rcu) isn't needed, so let's drop that as well.

## Which versions are affected by CVE-2026-98788?


## How do I fix CVE-2026-98788?

Apply the vendor's patch.

## Is CVE-2026-98788 being exploited?

There is no known exploitation of CVE-2026-98788 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98788 and fix it if it is affected.

What it is: CVE-2026-98788 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-2026-98788 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-2026-98788/ (Markdown: https://insights.sbomify.com/CVE-2026-98788/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98788
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98788
- OSV: https://osv.dev/vulnerability/CVE-2026-98788

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98788/
Summaries are generated and may contain mistakes; the official description above is the record.