Microsoft Confirms RoguePlanet Defender Zero

CVE-2026-33825 is an insufficient granularity of access control flaw (CWE-1220) in Microsoft Defender Antimalware Platform that allows an authorized attacker to elevate privileges locally. It is triggered by an attacker who already holds a low-privileged foothold on a machine running Defender, with no user interaction required. Successful exploitation has high impact on confidentiality, integrity, and availability (CVSS 3.1: 7.8), granting elevated local rights that facilitate defense evasion, persistence, or ransomware activity. Any organization running Microsoft Defender on Windows endpoints and servers is potentially affected. The flaw is actively exploited in the wild, was added to CISA's Known Exploited Vulnerabilities catalog on 2026-04-22 with ransomware use confirmed, and is one of three Microsoft Defender zero-days reported as exploited, two of which were still unpatched at the time of reporting.

Do: Apply Microsoft's April 2026 Patch Tuesday updates for the Defender Antimalware Platform (platform/security intelligence updates) per vendor instructions, consistent with CISA BOD 22-01 timelines for KEV entries, and note reports that two of the three exploited Defender zero-days were still unpatched, so monitor for follow-up fixes. Prioritize patching internet-reachable and high-value Windows hosts, and hunt for signs of local privilege escalation and ransomware precursor activity on systems that cannot be updated immediately.

CVE-2026-45498 is a denial-of-service flaw (CWE-400, uncontrolled resource consumption) in the Microsoft Defender antimalware platform, rated 7.5 (High) with a network attack vector and no privileges or user interaction required. A remote, unauthenticated attacker can trigger excessive resource consumption that disrupts the Defender service, with high impact on availability but no confidentiality or integrity impact per the CVSS scoring. An attacker gains the ability to crash, hang, or disable antimalware protection on targeted systems, potentially leaving endpoints temporarily unprotected. Any deployment of Microsoft Defender — which is the default antimalware on modern Windows and is also deployed as a cloud service — is in scope, and CISA's required action explicitly points defenders to BOD 22-01 guidance for cloud services. The flaw has been added to CISA's KEV catalog (2026-05-20), EPSS assigns it a 63.1% probability of exploitation within 30 days, and headlines confirm it is being exploited in the wild alongside CVE-2026-41091.

Do: Apply mitigations per Microsoft's vendor instructions and follow applicable CISA BOD 22-01 guidance for cloud services, as required by the KEV entry. Ensure the Defender antimalware platform and its security intelligence updates are fully current on all endpoints, and check event logs for Defender service crashes or disabled protection that may indicate exploitation. Ransomware use is currently listed as unknown, so treat any Defender outage on exposed systems as a potential precursor to follow-on activity.

Microsoft is aware of an elevation of privilege in the Microsoft Malware Protection Engine in Microsoft Defender publicly referred to as "RoguePlanet ".