# CVE-2026-64400: ksmbd: prevent path traversal bypass by restricting caseless retry

> A logic error in ksmbd allows attackers to bypass path restrictions and create files outside the share root via caseless retry flaws.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Jul 2026
- **Updated:** 21 Oct 2026
- **Also known as:** BELL-CVE-2026-64400, DEBIAN-CVE-2026-64400, GHSA-cg5c-7728-29v7, ROOT-OS-DEBIAN-12-CVE-2026-64400, ROOT-OS-DEBIAN-13-CVE-2026-64400, ROOT-OS-UBUNTU-2204-CVE-2026-64400, UBUNTU-CVE-2026-64400

## What is CVE-2026-64400?

CVE-2026-64400 is a high-severity path traversal vulnerability in Linux kernel, published on 25 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: prevent path traversal bypass by restricting caseless retry

ksmbd_vfs_path_lookup() enforces LOOKUP_BENEATH to restrict path
resolution within the share root. When a crafted path attempts to
escape the share boundary using parent-directory components ('..'),
vfs_path_parent_lookup() detects this and immediately fails,
returning -EXDEV.

However, a bug exists in __ksmbd_vfs_kern_path() under caseless mode.
The function fails to intercept the -EXDEV error and erroneously
falls through to the caseless retry logic, which is intended only
for genuinely missing files. During this retry process, the path
is reconstructed, leading to an unintended LOOKUP_BENEATH bypass
that allows write-capable users to create zero-length files or
directories outside the exported share.

Fix this by ensuring that the execution only proceeds to the caseless
lookup retry when the error is specifically -ENOENT. Any other errors,
such as -EXDEV from a path traversal attempt, must be returned immediately.

## Which versions are affected by CVE-2026-64400?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64400?

Apply the vendor's patch.

## Is CVE-2026-64400 being exploited?

There is no known exploitation of CVE-2026-64400 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-2026-64400 and fix it if it is affected.

What it is: CVE-2026-64400 is a high-severity path traversal vulnerability in Linux kernel, published on 25 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-64400 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-2026-64400/ (Markdown: https://insights.sbomify.com/CVE-2026-64400/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64400
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64400
- OSV: https://osv.dev/vulnerability/CVE-2026-64400

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64400/
Summaries are generated and may contain mistakes; the official description above is the record.