# CVE-2024-50220: fork: do not invoke uffd on fork if error occurs

> A race condition in the Linux kernel fork process allows exposing inconsistent memory states, potentially leading to system instability or crashes.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** 9 Nov 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2024-50220, DEBIAN-CVE-2024-50220, GHSA-cx44-8c8j-5rr2, UBUNTU-CVE-2024-50220

## What is CVE-2024-50220?

CVE-2024-50220 is a medium-severity vulnerability in Linux kernel, published on 9 Nov 2024. 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:

fork: do not invoke uffd on fork if error occurs

Patch series "fork: do not expose incomplete mm on fork".

During fork we may place the virtual memory address space into an
inconsistent state before the fork operation is complete.

In addition, we may encounter an error during the fork operation that
indicates that the virtual memory address space is invalidated.

As a result, we should not be exposing it in any way to external machinery
that might interact with the mm or VMAs, machinery that is not designed to
deal with incomplete state.

We specifically update the fork logic to defer khugepaged and ksm to the
end of the operation and only to be invoked if no error arose, and
disallow uffd from observing fork events should an error have occurred.

This patch (of 2):

Currently on fork we expose the virtual address space of a process to
userland unconditionally if uffd is registered in VMAs, regardless of
whether an error arose in the fork.

This is performed in dup_userfaultfd_complete() which is invoked
unconditionally, and performs two duties - invoking registered handlers
for the UFFD_EVENT_FORK event via dup_fctx(), and clearing down
userfaultfd_fork_ctx objects established in dup_userfaultfd().

This is problematic, because the virtual address space may not yet be
correctly initialised if an error arose.

The change in commit d24062914837 ("fork: use __mt_dup() to duplicate
maple tree in dup_mmap()") makes this more pertinent as we may be in a
state where entries in the maple tree are not yet consistent.

We address this by, on fork error, ensuring that we roll back state that
we would otherwise expect to clean up through the event being handled by
userland and perform the memory freeing duty otherwise performed by
dup_userfaultfd_complete().

We do this by implementing a new function, dup_userfaultfd_fail(), which
performs the same loop, only decrementing reference counts.

Note that we perform mmgrab() on the parent and child mm's, however
userfaultfd_ctx_put() will mmdrop() this once the reference count drops to
zero, so we will avoid memory leaks correctly here.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2024-50220?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-50220?

Apply the vendor's patch.

## Is CVE-2024-50220 being exploited?

There is no known exploitation of CVE-2024-50220 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-50220 and fix it if it is affected.

What it is: CVE-2024-50220 is a medium-severity vulnerability in Linux kernel, published on 9 Nov 2024. 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-2024-50220 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2024-50220/ (Markdown: https://insights.sbomify.com/CVE-2024-50220/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-50220
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-50220
- OSV: https://osv.dev/vulnerability/CVE-2024-50220

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-50220/
Summaries are generated and may contain mistakes; the official description above is the record.