# CVE-2026-31704: ksmbd: use check_add_overflow() to prevent u16 DACL size overflow

> An integer overflow in the Linux kernel's ksmbd module allows buffer corruption via crafted ACL entries, potentially leading to code execution or privilege escalation.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 1 May 2026
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2026-31704, DEBIAN-CVE-2026-31704, GHSA-xmgr-rx43-m3gf, ROOT-OS-DEBIAN-12-CVE-2026-31704, ROOT-OS-UBUNTU-2204-CVE-2026-31704, ROOT-OS-UBUNTU-2404-CVE-2026-31704, UBUNTU-CVE-2026-31704

## What is CVE-2026-31704?

CVE-2026-31704 is a medium-severity vulnerability in Linux kernel, published on 1 May 2026. 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:

ksmbd: use check_add_overflow() to prevent u16 DACL size overflow

set_posix_acl_entries_dacl() and set_ntacl_dacl() accumulate ACE sizes
in u16 variables. When a file has many POSIX ACL entries, the
accumulated size can wrap past 65535, causing the pointer arithmetic
(char *)pndace + *size to land within already-written ACEs. Subsequent
writes then overwrite earlier entries, and pndacl->size gets a
truncated value.

Use check_add_overflow() at each accumulation point to detect the
wrap before it corrupts the buffer, consistent with existing
check_mul_overflow() usage elsewhere in smbacl.c.

## Which versions are affected by CVE-2026-31704?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31704?

Apply the vendor's patch.

## Is CVE-2026-31704 being exploited?

There is no known exploitation of CVE-2026-31704 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-2026-31704 and fix it if it is affected.

What it is: CVE-2026-31704 is a medium-severity vulnerability in Linux kernel, published on 1 May 2026. 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-2026-31704 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-2026-31704/ (Markdown: https://insights.sbomify.com/CVE-2026-31704/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31704
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31704
- OSV: https://osv.dev/vulnerability/CVE-2026-31704

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31704/
Summaries are generated and may contain mistakes; the official description above is the record.