# CVE-2026-43490: ksmbd: validate inherited ACE SID length

> A memory corruption vulnerability in the Linux kernel's ksmbd SMB server allows attackers to execute code or cause denial of service via malformed ACEs.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 15 May 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2026-43490, DEBIAN-CVE-2026-43490, GHSA-9hm7-v4rj-6wqj, ROOT-OS-DEBIAN-12-CVE-2026-43490, ROOT-OS-UBUNTU-2204-CVE-2026-43490, ROOT-OS-UBUNTU-2404-CVE-2026-43490, UBUNTU-CVE-2026-43490

## What is CVE-2026-43490?

CVE-2026-43490 is a high-severity memory corruption vulnerability in Linux kernel, published on 15 May 2026. 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: validate inherited ACE SID length

smb_inherit_dacl() walks the parent directory DACL loaded from the
security descriptor xattr. It verifies that each ACE contains the fixed
SID header before using it, but does not verify that the variable-length
SID described by sid.num_subauth is fully contained in the ACE.

A malformed inheritable ACE can advertise more subauthorities than are
present in the ACE. compare_sids() may then read past the ACE.
smb_set_ace() also clamps the copied destination SID, but used the
unchecked source SID count to compute the inherited ACE size. That could
advance the temporary inherited ACE buffer pointer and nt_size accounting
past the allocated buffer.

Fix this by validating the parent ACE SID count and SID length before
using the SID during inheritance. Compute the inherited ACE size from the
copied SID so the size matches the bounded destination SID. Reject the
inherited DACL if size accumulation would overflow smb_acl.size or the
security descriptor allocation size.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-43490?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43490?

Apply the vendor's patch.

## Is CVE-2026-43490 being exploited?

There is no known exploitation of CVE-2026-43490 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-2026-43490 and fix it if it is affected.

What it is: CVE-2026-43490 is a high-severity memory corruption vulnerability in Linux kernel, published on 15 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-43490 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-2026-43490/ (Markdown: https://insights.sbomify.com/CVE-2026-43490/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43490
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43490
- OSV: https://osv.dev/vulnerability/CVE-2026-43490

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43490/
Summaries are generated and may contain mistakes; the official description above is the record.