# CVE-2023-54203: ksmbd: fix slab-out-of-bounds in init_smb2_rsp_hdr

> A slab-out-of-bounds read in the Linux kernel's ksmbd module allows attackers to cause a denial of service via crafted SMB1 requests.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:** 30 Dec 2025
- **Updated:** 5 Aug 2026
- **Also known as:** GHSA-92h7-9rvh-996h, UBUNTU-CVE-2023-54203

## What is CVE-2023-54203?

CVE-2023-54203 is a critical memory corruption vulnerability in Linux, published on 30 Dec 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:

ksmbd: fix slab-out-of-bounds in init_smb2_rsp_hdr

When smb1 mount fails, KASAN detect slab-out-of-bounds in
init_smb2_rsp_hdr like the following one.
For smb1 negotiate(56bytes) , init_smb2_rsp_hdr() for smb2 is called.
The issue occurs while handling smb1 negotiate as smb2 server operations.
Add smb server operations for smb1 (get_cmd_val, init_rsp_hdr,
allocate_rsp_buf, check_user_session) to handle smb1 negotiate so that
smb2 server operation does not handle it.

[  411.400423] CIFS: VFS: Use of the less secure dialect vers=1.0 is
not recommended unless required for access to very old servers
[  411.400452] CIFS: Attempting to mount \\192.168.45.139\homes
[  411.479312] ksmbd: init_smb2_rsp_hdr : 492
[  411.479323] ==================================================================
[  411.479327] BUG: KASAN: slab-out-of-bounds in
init_smb2_rsp_hdr+0x1e2/0x1f4 [ksmbd]
[  411.479369] Read of size 16 at addr ffff888488ed0734 by task kworker/14:1/199

[  411.479379] CPU: 14 PID: 199 Comm: kworker/14:1 Tainted: G
 OE      6.1.21 #3
[  411.479386] Hardware name: ASUSTeK COMPUTER INC. Z10PA-D8
Series/Z10PA-D8 Series, BIOS 3801 08/23/2019
[  411.479390] Workqueue: ksmbd-io handle_ksmbd_work [ksmbd]
[  411.479425] Call Trace:
[  411.479428]  <TASK>
[  411.479432]  dump_stack_lvl+0x49/0x63
[  411.479444]  print_report+0x171/0x4a8
[  411.479452]  ? kasan_complete_mode_report_info+0x3c/0x200
[  411.479463]  ? init_smb2_rsp_hdr+0x1e2/0x1f4 [ksmbd]
[  411.479497]  kasan_report+0xb4/0x130
[  411.479503]  ? init_smb2_rsp_hdr+0x1e2/0x1f4 [ksmbd]
[  411.479537]  kasan_check_range+0x149/0x1e0
[  411.479543]  memcpy+0x24/0x70
[  411.479550]  init_smb2_rsp_hdr+0x1e2/0x1f4 [ksmbd]
[  411.479585]  handle_ksmbd_work+0x109/0x760 [ksmbd]
[  411.479616]  ? _raw_spin_unlock_irqrestore+0x50/0x50
[  411.479624]  ? smb3_encrypt_resp+0x340/0x340 [ksmbd]
[  411.479656]  process_one_work+0x49c/0x790
[  411.479667]  worker_thread+0x2b1/0x6e0
[  411.479674]  ? process_one_work+0x790/0x790
[  411.479680]  kthread+0x177/0x1b0
[  411.479686]  ? kthread_complete_and_exit+0x30/0x30
[  411.479692]  ret_from_fork+0x22/0x30
[  411.479702]  </TASK>

## Which versions are affected by CVE-2023-54203?


## How do I fix CVE-2023-54203?

Apply the vendor's patch.

## Is CVE-2023-54203 being exploited?

There is no known exploitation of CVE-2023-54203 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-54203 and fix it if it is affected.

What it is: CVE-2023-54203 is a critical memory corruption vulnerability in Linux, published on 30 Dec 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-2023-54203 in the wild and no public exploit code.

Affected product: 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-2023-54203/ (Markdown: https://insights.sbomify.com/CVE-2023-54203/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-54203
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-54203
- OSV: https://osv.dev/vulnerability/CVE-2023-54203

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-54203/
Summaries are generated and may contain mistakes; the official description above is the record.