# CVE-2026-80778: futex/pi: Reject cross-mm private futex owners

> A use-after-free in the Linux kernel futex subsystem allows local attackers to escalate privileges or cause a denial of service.

- **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-2026-80778, DEBIAN-CVE-2026-80778, GHSA-pwhw-9cfc-qqqx, UBUNTU-CVE-2026-80778

## What is CVE-2026-80778?

CVE-2026-80778 is an use after free 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/pi: Reject cross-mm private futex owners

A private futex key borrows the waiter's mm without taking an mm_users
reference. Nevertheless, attach_to_pi_owner() currently accepts an owner
from a different address space and copies the private key into the owner's
PI state.

When that owner exits, exit_pi_state_list() uses the saved key to find the
hash bucket and acquires a reference to the waiter's private hash. If the
last user of the waiter's mm exits concurrently, futex_hash_free() frees
the hash while the owner still uses its bucket and reference.

Prevent this by validating in attach_to_pi_owner() that, for private
futexes, the owner mm and waiter mm are the same. Perform the check with
the owner's pi_lock held and after validating owner::futex::state to
serialize against a concurrent PI-state exit cleanup.

[ tglx: Amended comment ]

## Which versions are affected by CVE-2026-80778?


## How do I fix CVE-2026-80778?

Apply the vendor's patch.

## Is CVE-2026-80778 being exploited?

There is no known exploitation of CVE-2026-80778 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80778 and fix it if it is affected.

What it is: CVE-2026-80778 is an use after free 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-2026-80778 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-2026-80778/ (Markdown: https://insights.sbomify.com/CVE-2026-80778/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80778
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80778
- OSV: https://osv.dev/vulnerability/CVE-2026-80778

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80778/
Summaries are generated and may contain mistakes; the official description above is the record.