# CVE-2024-56740: nfs/localio: must clear res.replen in nfs_local_read_done

> A memory corruption vulnerability in the Linux kernel's NFSv3 LOCALIO implementation allows attackers to cause system crashes or potentially execute code.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 29 Dec 2024
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2024-56740, GHSA-24mf-qj78-vm87, UBUNTU-CVE-2024-56740

## What is CVE-2024-56740?

CVE-2024-56740 is a high-severity memory corruption vulnerability in Linux kernel, published on 29 Dec 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:

nfs/localio: must clear res.replen in nfs_local_read_done

Otherwise memory corruption can occur due to NFSv3 LOCALIO reads
leaving garbage in res.replen:
- nfs3_read_done() copies that into server->read_hdrsize; from there
  nfs3_proc_read_setup() copies it to args.replen in new requests.
- nfs3_xdr_enc_read3args() passes that to rpc_prepare_reply_pages()
  which includes it in hdrsize for xdr_init_pages, so that rq_rcv_buf
  contains a ridiculous len.
- This is copied to rq_private_buf and xs_read_stream_request()
  eventually passes the kvec to sock_recvmsg() which receives incoming
  data into entirely the wrong place.

This is easily reproduced with NFSv3 LOCALIO that is servicing reads
when it is made to pivot back to using normal RPC.  This switch back
to using normal NFSv3 with RPC can occur for a few reasons but this
issue was exposed with a test that stops and then restarts the NFSv3
server while LOCALIO is performing heavy read IO.

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

## Which versions are affected by CVE-2024-56740?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-56740?

Apply the vendor's patch.

## Is CVE-2024-56740 being exploited?

There is no known exploitation of CVE-2024-56740 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-2024-56740 and fix it if it is affected.

What it is: CVE-2024-56740 is a high-severity memory corruption vulnerability in Linux kernel, published on 29 Dec 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-2024-56740 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-2024-56740/ (Markdown: https://insights.sbomify.com/CVE-2024-56740/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-56740
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-56740
- OSV: https://osv.dev/vulnerability/CVE-2024-56740

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-56740/
Summaries are generated and may contain mistakes; the official description above is the record.