# CVE-2023-54085: mptcp: fix NULL pointer dereference on fastopen early fallback

> A NULL pointer dereference in the Linux kernel MPTCP fastopen path allows attackers to cause a denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Dec 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2023-54085, GHSA-459f-v5p8-p6w3, UBUNTU-CVE-2023-54085

## What is CVE-2023-54085?

CVE-2023-54085 is a high-severity vulnerability in Linux, published on 24 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

mptcp: fix NULL pointer dereference on fastopen early fallback

In case of early fallback to TCP, subflow_syn_recv_sock() deletes
the subflow context before returning the newly allocated sock to
the caller.

The fastopen path does not cope with the above unconditionally
dereferencing the subflow context.

## Which versions are affected by CVE-2023-54085?


## How do I fix CVE-2023-54085?

Apply the vendor's patch.

## Is CVE-2023-54085 being exploited?

There is no known exploitation of CVE-2023-54085 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-54085 and fix it if it is affected.

What it is: CVE-2023-54085 is a high-severity vulnerability in Linux, published on 24 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-54085 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-2023-54085/ (Markdown: https://insights.sbomify.com/CVE-2023-54085/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-54085
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-54085
- OSV: https://osv.dev/vulnerability/CVE-2023-54085

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-54085/
Summaries are generated and may contain mistakes; the official description above is the record.