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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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 include Linux kernel.
How do I fix CVE-2026-64400?
Apply the vendor's patch.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
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
Sources
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 and 1 more.