Security Policy Errors

How to Report a Fileless False Positive in Microsoft Defender

Adam Davis Oct 13, 2026 869 views

Question details

The user needs to report a repeatable fileless false positive detection to the Microsoft Defender team, but cannot use the standard portal because the diagnostic file is too large.

How to Report a Fileless False Positive in Microsoft Defender

Product: Microsoft Defender
Device & OS: not provided
Scenario: Attempting to submit diagnostic data for a fileless false positive using the Microsoft Defender submission portal.
Observed behavior: The submission portal rejects the diagnostic CAB file because it contains too many files or exceeds the upload limits.

Before you start

Ensure you have thoroughly documented the exact steps to reproduce the fileless false-positive detection and have your diagnostic CAB file ready before reaching out to support.

Solution 1Recommended

Escalate the False Positive via Microsoft Support

Since the submission portal limits are blocking the upload, bypassing the portal and directly opening a support ticket allows you to provide large diagnostic files and reach the analysis team.

The standard Microsoft Defender submission portal is optimized for typical file-based malware and standard false positives. When dealing with complex fileless detections, the generated diagnostic CAB files often exceed the portal's strict file count and size limits. Escaping these constraints requires direct intervention from the support team.

Sign in to Microsoft Support

Navigate to the official Microsoft Support contact page in your web browser and sign in using your Microsoft account credentials.

Describe the security issue

In the issue description box, clearly state that you are experiencing a repeatable fileless false positive in Microsoft Defender and that the submission portal is rejecting your diagnostic CAB file.

Initiate a support request

Select the 'Contact Support' button. Follow the on-screen prompts to choose your preferred contact method, such as live chat or requesting a callback.

Request analysis team escalation

Once connected with a support agent, explain the situation, offer to provide your diagnostic CAB file through their secure transfer tools, and explicitly request that the case be escalated to the Defender analysis team.

Escalate the False Positive via Microsoft Support

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Frequently Asked Questions

What is a fileless false positive in Microsoft Defender?

A fileless false positive occurs when Defender incorrectly flags an in-memory process, script, or legitimate system behavior as malicious, even though no traditional malware file exists on the hard drive.

Why does the Defender submission portal reject my CAB file?

The submission portal enforces strict limits on the number of files and the total file size per upload. Diagnostic CAB files for complex fileless detections often contain detailed system logs that exceed these predefined limits.

Can I manually reduce the size of the CAB file to bypass the limit?

While you could attempt to remove non-essential logs from the CAB file, fileless detections typically require comprehensive data for accurate analysis. Contacting support to submit the full file is the recommended approach to ensure the issue is resolved.

Microsoft Office Security Issues