# CVE-2026-45889: mptcp: do not account for OoO in mptcp_rcvbuf_grow()

> A race condition in the Linux kernel MPTCP implementation can cause a divide-by-zero error, leading to a system crash.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/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:** 27 May 2026
- **Updated:** 27 May 2026
- **Also known as:** BELL-CVE-2026-45889, DEBIAN-CVE-2026-45889, GHSA-gh29-fq9g-3p7h, UBUNTU-CVE-2026-45889

## What is CVE-2026-45889?

CVE-2026-45889 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 May 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:

mptcp: do not account for OoO in mptcp_rcvbuf_grow()

MPTCP-level OoOs are physiological when multiple subflows are active
concurrently and will not cause retransmissions nor are caused by
drops.

Accounting for them in mptcp_rcvbuf_grow() causes the rcvbuf slowly
drifting towards tcp_rmem[2].

Remove such accounting. Note that subflows will still account for TCP-level
OoO when the MPTCP-level rcvbuf is propagated.

This also closes a subtle and very unlikely race condition with rcvspace
init; active sockets with user-space holding the msk-level socket lock,
could complete such initialization in the receive callback, after that the
first OoO data reaches the rcvbuf and potentially triggering a divide by
zero Oops.

Weakness: CWE-369 (Divide By Zero)

## Which versions are affected by CVE-2026-45889?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-45889?

Apply the vendor's patch.

## Is CVE-2026-45889 being exploited?

There is no known exploitation of CVE-2026-45889 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-2026-45889 and fix it if it is affected.

What it is: CVE-2026-45889 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 May 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-2026-45889 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-2026-45889/ (Markdown: https://insights.sbomify.com/CVE-2026-45889/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45889
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45889
- OSV: https://osv.dev/vulnerability/CVE-2026-45889

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45889/
Summaries are generated and may contain mistakes; the official description above is the record.