Update on the Windows Defender zero-day situation: Huntress now confirms attackers are chaining the three flaws leaked April 3 by a researcher called 'Chaotic Eclipse' to deploy a custom tunneling agent named 'BeigeBurrow' on victim systems. Microsoft patched one of the three (BlueHammer, CVE-2026-33825) on April 14, but the other two are still unpatched two weeks later: RedSun lets attackers gain SYSTEM privileges even on patched machines, and UnDefend stops Defender from receiving signature updates - effectively turning off the antivirus. CISA gave federal agencies until May 6 to deploy the BlueHammer patch.
CISA added CVE-2026-33825 to its Known Exploited Vulnerabilities catalog on April 23 with a May 7 federal patch deadline. The flaw, nicknamed BlueHammer, is a race condition in Windows Defender's file-remediation logic that lets an unprivileged local attacker overwrite arbitrary files on disk and escalate to SYSTEM on fully-patched Windows 10 and Windows 11 hosts. It was patched in Microsoft's April 8 Patch Tuesday but a working proof-of-concept had already been published to GitHub by a researcher called 'Chaotic Eclipse' on April 7, before the fix shipped. Huntress Labs saw in-the-wild exploitation from April 10, with attackers also picking up two sibling Defender zero-days the same researcher leaked: RedSun (another local privilege escalation) and UnDefend (a denial-of-service that blocks Defender from pulling security definition updates, effectively disarming the EDR). Those two still have no Microsoft patch. The combination - a working privilege-escalation path plus an unpatched technique to silently cripple Defender itself - makes this a priority hunt, not just a priority patch.
Just days after Microsoft patched BlueHammer (CVE-2026-33825) in Tuesday's Patch Tuesday, the same researcher 'Chaotic Eclipse' (aka Nightmare-Eclipse) has released a second Microsoft Defender local privilege escalation zero-day called RedSun. The exploit works on fully-patched Windows 10, Windows 11, and Windows Server systems with Windows Defender enabled, even after installing this week's April updates. The flaw abuses Defender's cloud file rollback behavior: when Defender detects a file with a 'cloud tag' it tries to restore it to its original location without validating the target path. The exploit uses NTFS junctions and opportunistic locks to redirect the write to C:\Windows\System32, overwriting system files like TieringEngineService.exe to gain SYSTEM privileges. Huntress Labs is reporting all three recently-leaked Windows Defender zero-days (BlueHammer, RedSun, and UnDefend) are now being exploited in the wild. The researcher has threatened to drop more severe RCE exploits in protest of how Microsoft handled their disclosure process. No patch available for RedSun yet. Working PoC code is public on GitHub.
TrustStrike Labs