Microsoft Defender for Endpoint is currently experiencing a bug that generates false positive alerts concerning out-of-date Basic Input/Output System (BIOS) versions, primarily affecting Dell devices.
The issue, tracked by Microsoft under the reference ID DZ1163521, is causing security teams to receive notifications to update device firmware that is already current.
This has led to confusion and unnecessary administrative overhead for organizations relying on the endpoint security platform for vulnerability management. Microsoft has confirmed the problem and is actively working on a resolution.
The bug specifically impacts organizations that use Microsoft Defender for Endpoint to monitor their devices of Dell hardware. Affected users and security administrators are receiving persistent alerts indicating that a device’s BIOS is vulnerable and requires an update.
However, upon investigation, it is discovered that the BIOS version on the flagged device is already the latest version available from Dell.
Flood of False BIOS Alerts
This flood of erroneous alerts creates significant operational challenges, including alert fatigue among security analysts, who may become desensitized to legitimate threats.
Furthermore, it consumes valuable time and resources as IT teams are forced to investigate and validate these non-issues, diverting their attention from genuine security incidents.
Microsoft has investigated the incident and identified the root cause as a code bug within the Defender for Endpoint service. According to their update, the flaw resides in the specific logic responsible for fetching and evaluating vulnerability information related to Dell devices.
This faulty code incorrectly interprets the BIOS version data from the endpoints, leading it to misidentify up-to-date systems as vulnerable.
The problem highlights the complexities involved in accurately managing vendor-specific firmware and software versions across a diverse range of hardware within a centralized security monitoring solution.
The issue is not a vulnerability in the Dell BIOS itself but rather a processing error within Microsoft’s security platform.
In a communication update released on October 2, 2025, Microsoft confirmed that its engineering team has successfully developed a fix to address the code bug.
While the issue’s status remains “OPEN,” the company is now preparing to deploy the corrective patch to the affected environment. Microsoft has indicated that it anticipates the deployment will commence around the time of its next scheduled update.
Organizations impacted by this event are advised to monitor the Microsoft service health dashboard for advisory DZ1163521 for the latest information on the fix rollout.
Until the patch is fully deployed, administrators will need to manually verify the BIOS status of flagged Dell devices to distinguish these false positives from legitimate threats.
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