CVE-2026-64918 Microsoft CVE debrief

Who should care

Defenders responsible for Microsoft Office and Microsoft 365 deployments should assess their exposure, especially in environments with external or untrusted network access. This includes IT security teams, system administrators, and network security engineers.

Why it matters

This vulnerability allows an unauthorized attacker to perform spoofing over a network, potentially leading to security breaches in affected Microsoft Office and Microsoft 365 deployments.

• Verify exposure in Office and Microsoft 365 deployments.
• Apply security updates to prevent exploitation.
• Monitor network activity for suspicious spoofing attempts.
• Update incident response plans to address potential spoofing attacks.

Technical summary

The vulnerability exists due to insufficiently protected credentials in Microsoft Office, allowing an unauthorized attacker to perform spoofing over a network. Affected products include Microsoft 365 Apps for Enterprise, Microsoft Office 2016, Microsoft Office 2019, Microsoft Office LTSC 2021, and Microsoft Office LTSC 2024.

Defensive priority

Defenders should prioritize verifying exposure in their Office and Microsoft 365 deployments, especially where external or untrusted network access is possible.

Recommended defensive actions

• Verify Office and Microsoft 365 deployments for exposure, especially where external access is possible.
• Apply security updates from Microsoft as available.
• Monitor network activity for suspicious spoofing attempts.
• Review and update incident response plans to address potential spoofing attacks.

Evidence notes

The CVE Program and NVD provide official records of this vulnerability. Microsoft has released a security update guide for this issue. The vulnerability is confirmed to affect multiple versions of Microsoft Office and Microsoft 365 Apps for Enterprise. Defenders should verify their deployments for exposure, especially where external access is possible, and apply security updates as available. The official CVE record and NVD detail page provide further information on 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.