CVE-2026-64400
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.
CSIRTS triage
- What
- This vulnerability prevents path traversal bypass by restricting caseless retry.
- Who is affected
- Deployments using the ksmbd server.
- Urgency
- Remediation is critical to prevent unauthorized file access, although no exploitation has been reported.
- Action
- Apply the patch for CVE-2026-64400.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.36% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 28% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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