# CVE-2025-38523: cifs: Fix the smbd_response slab to allow usercopy

> A kernel bug in the CIFS RDMA client causes a crash when hardened usercopy is enabled, leading to denial of service.

- **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:** Yes
- **Published:** 16 Aug 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-38523, DEBIAN-CVE-2025-38523, GHSA-4x9v-h3r3-c3mf, UBUNTU-CVE-2025-38523

## What is CVE-2025-38523?

CVE-2025-38523 is a high-severity vulnerability in Linux kernel, published on 16 Aug 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:

cifs: Fix the smbd_response slab to allow usercopy

The handling of received data in the smbdirect client code involves using
copy_to_iter() to copy data from the smbd_reponse struct's packet trailer
to a folioq buffer provided by netfslib that encapsulates a chunk of
pagecache.

If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks
then performed in copy_to_iter() oopsing with something like the following:

 CIFS: Attempting to mount //172.31.9.1/test
 CIFS: VFS: RDMA transport established
 usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)!
 ------------[ cut here ]------------
 kernel BUG at mm/usercopy.c:102!
 ...
 RIP: 0010:usercopy_abort+0x6c/0x80
 ...
 Call Trace:
  <TASK>
  __check_heap_object+0xe3/0x120
  __check_object_size+0x4dc/0x6d0
  smbd_recv+0x77f/0xfe0 [cifs]
  cifs_readv_from_socket+0x276/0x8f0 [cifs]
  cifs_read_from_socket+0xcd/0x120 [cifs]
  cifs_demultiplex_thread+0x7e9/0x2d50 [cifs]
  kthread+0x396/0x830
  ret_from_fork+0x2b8/0x3b0
  ret_from_fork_asm+0x1a/0x30

The problem is that the smbd_response slab's packet field isn't marked as
being permitted for usercopy.

Fix this by passing parameters to kmem_slab_create() to indicate that
copy_to_iter() is permitted from the packet region of the smbd_response
slab objects, less the header space.

Weakness: CWE-1188 (Initialization of a Resource with an Insecure Default)

## Which versions are affected by CVE-2025-38523?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-38523?

Apply the vendor's patch.

## Is CVE-2025-38523 being exploited?

There is no known exploitation of CVE-2025-38523 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-2025-38523 and fix it if it is affected.

What it is: CVE-2025-38523 is a high-severity vulnerability in Linux kernel, published on 16 Aug 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-2025-38523 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-2025-38523/ (Markdown: https://insights.sbomify.com/CVE-2025-38523/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38523
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38523
- OSV: https://osv.dev/vulnerability/CVE-2025-38523

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38523/
Summaries are generated and may contain mistakes; the official description above is the record.