A recent update to Windows 10’s Microsoft Defender antivirus solution allows it to download malware and other files to a Windows computer. Microsoft Defender is now part of the long list of Windows programs that can be abused by local attackers. Microsoft told BleepingComputer that it will still protect customers from malware. The good news is that Microsoft Defender will detect malicious files downloaded with MpCmdRun.exe, but it is unknown if other AV software will allow this program to bypass their detections. With this discovery, administrators and blue teamers now have an additional Windows executable that they need to monitor.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-defender-can-ironically-be-used-to-download-malware/