# CVE-2026-80775: futex: Fix race on the initial mm->futex.phash.ref allocation

> A race condition in the Linux kernel futex subsystem allows local attackers to trigger use-after-free, potentially leading to privilege escalation or code execution.

- **Severity:** Not scored
- **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:** 4 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-80775, DEBIAN-CVE-2026-80775, GHSA-f29q-mg8h-pcrg, UBUNTU-CVE-2026-80775

## What is CVE-2026-80775?

CVE-2026-80775 is a vulnerability in Linux, published on 4 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:

futex: Fix race on the initial mm->futex.phash.ref allocation

futex_hash_allocate() allocates mm->futex.phash.ref without any locking.
Commit d9b05321e21e ("futex: Move futex_hash_free() back to __mmput()")
moved the allocation here and assumed that the process has just a single
thread at this point.

Commit ee9dce44362b ("futex: Drop CLONE_THREAD requirement for private
default hash alloc") widened need_futex_hash_allocate_default() to cover
any CLONE_VM clone, but left out vfork because the parent is suspended and
cannot race.

That no longer holds once vfork is nested. If a vfork child calls vfork
again and is then killed with SIGKILL, the parent is released from its
vfork wait and runs concurrently with the grandchild in the same mm.
Neither of them went through futex_hash_allocate_default().

When both call prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_SET_SLOTS) at the same
time, each one sees mm->futex.phash.ref as NULL and stores its own percpu
counter. Only the last store survives. The counter stored first is no
longer reachable from the mm, so the references on it are not seen by
__futex_ref_atomic_end(). A private hash that still has references is then
considered dead and freed, and a task that still holds one of its buckets
writes into freed memory in futex_q_lock().

Store the counter once with cmpxchg() and let the loser free_percpu() its
own. The initial reference has to be taken before the store, otherwise
another task can install a private hash while the counter is still 0.

## Which versions are affected by CVE-2026-80775?


## How do I fix CVE-2026-80775?

Apply the vendor's patch.

## Is CVE-2026-80775 being exploited?

There is no known exploitation of CVE-2026-80775 in the wild and no public exploit code.

Public exploit code:

- Android/ARM64 port (github_poc): https://github.com/ylh440104/InfinityCore-Android-CVE-2026-80775

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80775 and fix it if it is affected.

What it is: CVE-2026-80775 is a vulnerability in Linux, published on 4 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-2026-80775 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-2026-80775/ (Markdown: https://insights.sbomify.com/CVE-2026-80775/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80775
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80775
- OSV: https://osv.dev/vulnerability/CVE-2026-80775

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80775/
Summaries are generated and may contain mistakes; the official description above is the record.