CVE-2026-64400

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References