# CVE-2025-21994: ksmbd: fix incorrect validation for num_aces field of smb_acl

> An integer overflow in the Linux kernel's ksmbd module allows attackers to cause a denial of service via crafted SMB requests.

- **Severity:** High 7.6 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 Apr 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-21994, DEBIAN-CVE-2025-21994, GHSA-pcv3-r2v8-4964, ROOT-OS-UBUNTU-2404-CVE-2025-21994, UBUNTU-CVE-2025-21994

## What is CVE-2025-21994?

CVE-2025-21994 is a high-severity vulnerability in Linux kernel, published on 2 Apr 2025. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix incorrect validation for num_aces field of smb_acl

parse_dcal() validate num_aces to allocate posix_ace_state_array.

if (num_aces > ULONG_MAX / sizeof(struct smb_ace *))

It is an incorrect validation that we can create an array of size ULONG_MAX.
smb_acl has ->size field to calculate actual number of aces in request buffer
size. Use this to check invalid num_aces.

## Which versions are affected by CVE-2025-21994?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21994?

Apply the vendor's patch.

## Is CVE-2025-21994 being exploited?

There is no known exploitation of CVE-2025-21994 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-2025-21994 and fix it if it is affected.

What it is: CVE-2025-21994 is a high-severity vulnerability in Linux kernel, published on 2 Apr 2025. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-21994 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-2025-21994/ (Markdown: https://insights.sbomify.com/CVE-2025-21994/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21994
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21994
- OSV: https://osv.dev/vulnerability/CVE-2025-21994

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21994/
Summaries are generated and may contain mistakes; the official description above is the record.