A new zero-day vulnerability in Microsoft Defender has been disclosed by a researcher known as "Chaotic Eclipse," who has created a proof-of-concept exploit called "RedSun." This vulnerability allows local privilege escalation to SYSTEM level on Windows 10, Windows 11, and Windows Server when Microsoft Defender is active. The vulnerability has attracted attention from antivirus vendors, with some detecting it on VirusTotal due to an embedded EIRCAR in the executable. Chaotic Eclipse previously disclosed another vulnerability named BlueHammer, which also allowed local attackers to gain SYSTEM or elevated permissions. The researcher expressed dissatisfaction with Microsoft's vulnerability disclosure process, recounting negative interactions with the company. A Microsoft spokesperson stated the company's commitment to investigating security issues and supporting coordinated vulnerability disclosure.