# CVE-2021-47132: mptcp: fix sk_forward_memory corruption on retransmission

> A race condition in the Linux kernel MPTCP implementation can corrupt memory, potentially leading to denial of service or code execution.

- **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:** No
- **Published:** 15 Mar 2024
- **Updated:** 5 Aug 2026
- **Also known as:** GHSA-48qq-74v6-m9rv, UBUNTU-CVE-2021-47132

## What is CVE-2021-47132?

CVE-2021-47132 is a high-severity memory corruption vulnerability in Linux kernel, published on 15 Mar 2024. 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 sk_forward_memory corruption on retransmission

MPTCP sk_forward_memory handling is a bit special, as such field
is protected by the msk socket spin_lock, instead of the plain
socket lock.

Currently we have a code path updating such field without handling
the relevant lock:

__mptcp_retrans() -> __mptcp_clean_una_wakeup()

Several helpers in __mptcp_clean_una_wakeup() will update
sk_forward_alloc, possibly causing such field corruption, as reported
by Matthieu.

Address the issue providing and using a new variant of blamed function
which explicitly acquires the msk spin lock.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2021-47132?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47132?

No fix has been published for CVE-2021-47132 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-47132 being exploited?

There is no known exploitation of CVE-2021-47132 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-2021-47132 and fix it if it is affected.

What it is: CVE-2021-47132 is a high-severity memory corruption vulnerability in Linux kernel, published on 15 Mar 2024. 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-2021-47132 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-2021-47132/ (Markdown: https://insights.sbomify.com/CVE-2021-47132/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47132
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47132
- OSV: https://osv.dev/vulnerability/CVE-2021-47132

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47132/
Summaries are generated and may contain mistakes; the official description above is the record.