ksmbd: prevent path traversal bypass by restricting caseless retry
CVE-2026-64400 · published 25 Jul 2026
How serious is it
- Severity: high, CVSS score 8.6 out of 10.
- No exploit prediction (EPSS) score yet.
- Not on the CISA list of exploited vulnerabilities.
- No public exploit in Exploit-DB.
Is your app affected by CVE-2026-64400?
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Who is affected
- Linux Linux: 74d7970febf7e9005375aeda0df821d2edffc9f7 to < eec1dd2586c4016b7555a5d047db2b3756459fb2, 74d7970febf7e9005375aeda0df821d2edffc9f7 to < a1c331d98313380c38f616c8b28b890ec8ef9c28, 74d7970febf7e9005375aeda0df821d2edffc9f7 to < cfb5a56c218888f9d74165dff0c282cd0be97983, 74d7970febf7e9005375aeda0df821d2edffc9f7 to < 8c9a4f1327eb71efbf14842e7b8a6d965077eb67
- Linux Linux: 6.4
How to check
- Find out whether you run the affected product and which version, then compare it with the versions above.
How to fix
Copies a prompt for Claude Code, Cursor or Codex that asks it to check whether you run this product.
- Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
- If a vulnerable version was live, check your logs and rotate the secrets that server could read.
The advisory
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.
Check your whole app
Dependencies are only half of it. Free and read-only: before you push, run npx shippable-dev scan localhost:3000 in your project folder, no account needed. For your live app, you prove it's yours with a one-line tag first.
References
- git.kernel.org/stable/c/eec1dd2586c4016b7555a5d047db2b3756459fb2
- git.kernel.org/stable/c/a1c331d98313380c38f616c8b28b890ec8ef9c28
- git.kernel.org/stable/c/cfb5a56c218888f9d74165dff0c282cd0be97983
- git.kernel.org/stable/c/8c9a4f1327eb71efbf14842e7b8a6d965077eb67
- git.kernel.org/stable/c/54bab9ba5a9f156ffa9324fcbe5a356fd0242f95
Merged from CVE List. Last updated 25 Oct 2026. All vulnerabilities · RSS · JSON