# CVE-2026-90153: ksmbd: bound smb_check_perm_dacl() ACE walks by DACL size

> A flaw in the Linux kernel ksmbd server allows attackers to bypass access controls by crafting DACLs, potentially leading to unauthorized data access or privilege escalation.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N`)
- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102458, BELL-CVE-2026-90153, DEBIAN-CVE-2026-90153, GHSA-wffx-7972-vw67, UBUNTU-CVE-2026-90153

## What is CVE-2026-90153?

CVE-2026-90153 is a high-severity missing authorization vulnerability in Linux, published on 17 Sep 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: bound smb_check_perm_dacl() ACE walks by DACL size

smb_check_perm_dacl() validates that the DACL fits inside the NT
security descriptor, but then bounds its two ACE walks by the
remaining NTSD length (acl_size) rather than the DACL's declared
size (pdacl_size).

When pdacl->size is smaller than the trailing NTSD buffer, bytes
after the declared DACL boundary - still inside the stored security
descriptor - are parsed as ACEs during access checks.  A crafted
DACL can place an access-granting ACE beyond pdacl->size, and the
current code accepts it during SMB2_CREATE access validation, while
parse_dacl() and smb_inherit_dacl() stop at pdacl_size.

Bound both ACE walks by pdacl_size to match the DACL boundary
semantics used elsewhere in the server.

Validation:
- semantic KUnit harness shows the post-boundary ACE is selected
  before the fix and rejected (EACCES) after it
- linux master (7.2-rc6), x86_64

## Which versions are affected by CVE-2026-90153?


## How do I fix CVE-2026-90153?

Apply the vendor's patch.

## Is CVE-2026-90153 being exploited?

There is no known exploitation of CVE-2026-90153 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90153 and fix it if it is affected.

What it is: CVE-2026-90153 is a high-severity missing authorization vulnerability in Linux, published on 17 Sep 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-2026-90153 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-2026-90153/ (Markdown: https://insights.sbomify.com/CVE-2026-90153/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90153
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90153
- OSV: https://osv.dev/vulnerability/CVE-2026-90153

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90153/
Summaries are generated and may contain mistakes; the official description above is the record.