# CVE-2024-26638: nbd: always initialize struct msghdr completely

> An uninitialized memory bug in the Linux kernel's Network Block Device driver could allow local attackers to read sensitive kernel memory.

- **Severity:** Medium 4.4 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Mar 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2024-26638, DEBIAN-CVE-2024-26638, GHSA-c8gp-pfr5-2mm3, UBUNTU-CVE-2024-26638

## What is CVE-2024-26638?

CVE-2024-26638 is a medium-severity vulnerability in Linux kernel, published on 18 Mar 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:

nbd: always initialize struct msghdr completely

syzbot complains that msg->msg_get_inq value can be uninitialized [1]

struct msghdr got many new fields recently, we should always make
sure their values is zero by default.

[1]
 BUG: KMSAN: uninit-value in tcp_recvmsg+0x686/0xac0 net/ipv4/tcp.c:2571
  tcp_recvmsg+0x686/0xac0 net/ipv4/tcp.c:2571
  inet_recvmsg+0x131/0x580 net/ipv4/af_inet.c:879
  sock_recvmsg_nosec net/socket.c:1044 [inline]
  sock_recvmsg+0x12b/0x1e0 net/socket.c:1066
  __sock_xmit+0x236/0x5c0 drivers/block/nbd.c:538
  nbd_read_reply drivers/block/nbd.c:732 [inline]
  recv_work+0x262/0x3100 drivers/block/nbd.c:863
  process_one_work kernel/workqueue.c:2627 [inline]
  process_scheduled_works+0x104e/0x1e70 kernel/workqueue.c:2700
  worker_thread+0xf45/0x1490 kernel/workqueue.c:2781
  kthread+0x3ed/0x540 kernel/kthread.c:388
  ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

Local variable msg created at:
  __sock_xmit+0x4c/0x5c0 drivers/block/nbd.c:513
  nbd_read_reply drivers/block/nbd.c:732 [inline]
  recv_work+0x262/0x3100 drivers/block/nbd.c:863

CPU: 1 PID: 7465 Comm: kworker/u5:1 Not tainted 6.7.0-rc7-syzkaller-00041-gf016f7547aee #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
Workqueue: nbd5-recv recv_work

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2024-26638?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-26638?

Apply the vendor's patch.

## Is CVE-2024-26638 being exploited?

There is no known exploitation of CVE-2024-26638 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-2024-26638 and fix it if it is affected.

What it is: CVE-2024-26638 is a medium-severity vulnerability in Linux kernel, published on 18 Mar 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-2024-26638 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-2024-26638/ (Markdown: https://insights.sbomify.com/CVE-2024-26638/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-26638
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-26638
- OSV: https://osv.dev/vulnerability/CVE-2024-26638

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-26638/
Summaries are generated and may contain mistakes; the official description above is the record.