Linux Kernel up to 7.1.3 Ksmbd __ksmbd_vfs_kern_path path traversal

Summaryinfo

A vulnerability categorized as very critical has been discovered in Linux Kernel up to 7.1.3. This vulnerability affects the function __ksmbd_vfs_kern_path of the component Ksmbd. Executing a manipulation can lead to path traversal. This vulnerability appears as CVE-2026-64400. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 7.1.3 and classified as very critical. This vulnerability affects the function __ksmbd_vfs_kern_path of the component Ksmbd. The manipulation with an unknown input leads to a path traversal vulnerability. The CWE definition for the vulnerability is CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2026-64400 since 07/19/2026. The exploitation appears to be easy. The attack can be initiated remotely. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 07/25/2026). The MITRE ATT&CK project declares the attack technique as T1006.

Upgrading to version 7.1.4 or 7.2-rc1 eliminates this vulnerability. Applying the patch 8c9a4f1327eb71efbf14842e7b8a6d965077eb67/54bab9ba5a9f156ffa9324fcbe5a356fd0242f95 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.1.0
• 7.1.1
• 7.1.2
• 7.1.3

License

• open-source

Website

• Vendor: https://www.kernel.org/

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