CVE-2026-64389 Linux CVE debrief

Who should care

Linux kernel administrators and users, particularly those using SMB3 multichannel binding, should assess exposure and verify authentication mechanisms. Affected operator, platform, vulnerability-management, and security-team impact should be evaluated to ensure proper mitigation and remediation.

Why it matters

This vulnerability allows an attacker to modify the session key before authentication failure is returned, potentially leading to authentication bypass. Linux kernel administrators and users, particularly those using SMB3 multichannel binding, should assess exposure and verify authentication mechanisms.

• Potential authentication bypass
• Session key modification before authentication failure
• Possible elevation of privileges

Technical summary

The vulnerability is in the ksmbd implementation in the Linux kernel. The ksmbd_auth_ntlmv2() function derives the NTLMv2 session key into sess->sess_key before verifying the NTLMv2 response. This allows an attacker to modify the session key before authentication failure is returned. The issue arises from the derivation of the NTLMv2 session key into sess->sess_key before verifying the NTLMv2 response. This vulnerability has been resolved by deriving the base session key into a local buffer and copying it to sess->sess_key only after the proof matches.

Defensive priority

High

Recommended defensive actions

• Review and apply patches for the affected Linux kernel versions
• Verify authentication mechanisms for ksmbd
• Monitor for potential authentication bypass attempts
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and NVD vulnerability detail provide information on the vulnerability, its impact, and the affected versions of the Linux kernel. The source references provide patch information. Linux kernel administrators should verify authentication mechanisms for ksmbd and review patches for affected versions. Evidence limits suggest that further verification is required to confirm the scope of the vulnerability.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.