CVE-2026-64391
Linux kernel ksmbd credential bug allows unauthorized SMB alternate data stream access.
Is CVE-2026-64391 being exploited?
Not confirmed. CVE-2026-64391 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.46% probability of exploitation in the next 30 days.
How severe is CVE-2026-64391?
CVE-2026-64391 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-64391?
Yes. A fix has been recorded for CVE-2026-64391. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-64391 affect?
CVE-2026-64391 affects Linux kernel (ksmbd SMB server enabled), Distributions shipping ksmbd module. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-64391?
Update kernel/ksmbd packages from vendor immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote SMB clients can read/write NTFS alternate data streams (xattrs) using wrong creds, enabling data theft or tampering via ksmbd.
Patch when possible
- affected>= f44158485826c076335d6860d35872271a83791d and < a8f5d39971bbad9340d49cd41b0e2da9452a649d
- affected>= f44158485826c076335d6860d35872271a83791d and < 2b4592cea214683de0f2ce6f8c22c097fb0ea1ab
- affected>= f44158485826c076335d6860d35872271a83791d and < 52a56cf53ec834c44ac1b4d16d585f26613ee5ce
- affected>= f44158485826c076335d6860d35872271a83791d and < baa5e094886fffa7e6272edcb5e08be5ce28262c
- affected5.15
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.