# CVE-2025-23145: mptcp: fix NULL pointer in can_accept_new_subflow

> A race condition in the Linux kernel MPTCP implementation causes a null pointer dereference and kernel panic when processing concurrent SYN-ACK packets.

- **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:** 1 May 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2025-23145, DEBIAN-CVE-2025-23145, GHSA-3r7x-52q9-w4pw, ROOT-OS-DEBIAN-12-CVE-2025-23145, ROOT-OS-UBUNTU-2204-CVE-2025-23145, ROOT-OS-UBUNTU-2404-CVE-2025-23145, UBUNTU-CVE-2025-23145

## What is CVE-2025-23145?

CVE-2025-23145 is a high-severity vulnerability in Debian Debian Linux, published on 1 May 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 in can_accept_new_subflow

When testing valkey benchmark tool with MPTCP, the kernel panics in
'mptcp_can_accept_new_subflow' because subflow_req->msk is NULL.

Call trace:

  mptcp_can_accept_new_subflow (./net/mptcp/subflow.c:63 (discriminator 4)) (P)
  subflow_syn_recv_sock (./net/mptcp/subflow.c:854)
  tcp_check_req (./net/ipv4/tcp_minisocks.c:863)
  tcp_v4_rcv (./net/ipv4/tcp_ipv4.c:2268)
  ip_protocol_deliver_rcu (./net/ipv4/ip_input.c:207)
  ip_local_deliver_finish (./net/ipv4/ip_input.c:234)
  ip_local_deliver (./net/ipv4/ip_input.c:254)
  ip_rcv_finish (./net/ipv4/ip_input.c:449)
  ...

According to the debug log, the same req received two SYN-ACK in a very
short time, very likely because the client retransmits the syn ack due
to multiple reasons.

Even if the packets are transmitted with a relevant time interval, they
can be processed by the server on different CPUs concurrently). The
'subflow_req->msk' ownership is transferred to the subflow the first,
and there will be a risk of a null pointer dereference here.

This patch fixes this issue by moving the 'subflow_req->msk' under the
`own_req == true` conditional.

Note that the !msk check in subflow_hmac_valid() can be dropped, because
the same check already exists under the own_req mpj branch where the
code has been moved to.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2025-23145?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-23145?

Apply the vendor's patch.

## Is CVE-2025-23145 being exploited?

There is no known exploitation of CVE-2025-23145 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-23145 and fix it if it is affected.

What it is: CVE-2025-23145 is a high-severity vulnerability in Debian Debian Linux, published on 1 May 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-2025-23145 in the wild and no public exploit code.

Affected product: Debian Debian 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-2025-23145/ (Markdown: https://insights.sbomify.com/CVE-2025-23145/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-23145
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-23145
- OSV: https://osv.dev/vulnerability/CVE-2025-23145

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-23145/
Summaries are generated and may contain mistakes; the official description above is the record.