# CVE-2026-64394: ksmbd: add a WRITE_DAC/WRITE_OWNER check to SMB2 SET_INFO SECURITY

> Attackers can bypass access controls in ksmbd to rewrite file permissions and ownership, enabling unauthorized data modification and privilege escalation.

- **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:** 25 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-64394, DEBIAN-CVE-2026-64394, GHSA-hj5q-pp4q-jpfg, ROOT-OS-DEBIAN-12-CVE-2026-64394, ROOT-OS-UBUNTU-2204-CVE-2026-64394, UBUNTU-CVE-2026-64394

## What is CVE-2026-64394?

CVE-2026-64394 is a high-severity missing authorization vulnerability in Linux kernel, published on 25 Jul 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: add a WRITE_DAC/WRITE_OWNER check to SMB2 SET_INFO SECURITY

commit cc57232cae23 ("ksmbd: fix FSCTL permission bypass by adding a
permission check for FSCTL_SET_SPARSE") added a fp->daccess gate to
fsctl_set_sparse and noted that "similar handle-level checks exist in other
functions but are missing here." The SMB2 SET_INFO SECURITY arm is one of
the missing ones, and the most security-relevant: smb2_set_info_sec() calls
set_info_sec() with no per-handle access check.

set_info_sec() (fs/smb/server/smbacl.c) re-permissions the file: it
rewrites owner/group/mode via notify_change(), rewrites the POSIX ACL via
set_posix_acl(), and on KSMBD_SHARE_FLAG_ACL_XATTR shares removes and
rewrites the Windows security descriptor via ksmbd_vfs_set_sd_xattr().
Every other persistent-mutation arm of the sibling handler
smb2_set_info_file() checks fp->daccess first (FILE_WRITE_DATA /
FILE_DELETE / FILE_WRITE_EA / FILE_WRITE_ATTRIBUTES); the SECURITY arm —
which mutates the access control itself — is the only one with no gate.

A client can therefore open a handle with FILE_WRITE_ATTRIBUTES only (no
FILE_WRITE_DAC / FILE_WRITE_OWNER) and use SMB2_SET_INFO with InfoType
SMB2_O_INFO_SECURITY to rewrite the file's DACL and owner, granting itself
access the handle's daccess never carried. Unlike the FSCTL data arms this
is a metadata/xattr operation, so there is no FMODE_WRITE VFS backstop —
the missing fp->daccess check is the entire gate.

Setting a security descriptor is the WRITE_DAC / WRITE_OWNER operation, so
require at least one of those on the handle before re-permissioning the
file. -EACCES is mapped to STATUS_ACCESS_DENIED by smb2_set_info().

## Which versions are affected by CVE-2026-64394?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64394?

Apply the vendor's patch.

## Is CVE-2026-64394 being exploited?

There is no known exploitation of CVE-2026-64394 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-2026-64394 and fix it if it is affected.

What it is: CVE-2026-64394 is a high-severity missing authorization vulnerability in Linux kernel, published on 25 Jul 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-2026-64394 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-2026-64394/ (Markdown: https://insights.sbomify.com/CVE-2026-64394/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64394
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64394
- OSV: https://osv.dev/vulnerability/CVE-2026-64394

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64394/
Summaries are generated and may contain mistakes; the official description above is the record.