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

CVE-2026-64400 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-64400, released August 7, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-64400
- Priority: High
- CVSS: 8.6 (Moderate)
- EPSS: 0.0045
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 25, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-64400

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-64400](https://patchblox.com/security/data/fix/linux/debian-cve-2026-64400.md) | Aug 7, 2026 |
| Linux | linux Debian 14 | 7.1.4-1 | [DEBIAN-CVE-2026-64400](https://patchblox.com/security/data/fix/linux/debian-cve-2026-64400.md) | Aug 7, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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