Microsoft Defender Antimalware Platform EUVD-2026-22643

Attacker must possess valid low-privileged local user credentials on a Windows system running vulnerable Microsoft Defender Antimalware Platform version 4.0.0.0 through 4.18.26030.3010. The CVSS vector AV:L/AC:L/PR:L/UI:N indicates local access vector with low attack complexity, low privileges required, and no user interaction needed. Exploitation limits: Remote attack not possible - attacker must have existing local shell access (via RDP, physical access, or prior compromise). Default configurations are vulnerable without requiring specific feature enablement. Successful exploitation grants elevated privileges within the local system scope (S:U) but does not extend to other systems or security contexts. The vulnerability is constrained to Windows platforms where Microsoft Defender Antimalware Platform is deployed; other operating systems running different antimalware solutions are not affected through this specific CVE.

Real-world risk assessment reveals moderate-to-high technical severity but limited exploitation likelihood based on multi-source signals. CVSS 7.8 indicates a high-impact local privilege escalation (AV:L/AC:L/PR:L) with complete compromise of confidentiality, integrity, and availability in the local scope. However, EPSS probability of 0.04% (12th percentile) suggests security researchers and attackers have not widely adopted this vulnerability for exploitation campaigns. No CISA KEV listing indicates no confirmed active exploitation in the wild. The requirement for prior local authenticated access (PR:L) significantly constrains attack scenarios - an adversary must already have a foothold on the target system. For enterprise environments with Microsoft Defender deployed, this represents a realistic post-compromise escalation path but not an initial access vector. Priority should be HIGH for systems where local users are untrusted (multi-user servers, privileged access workstations) and MEDIUM for single-user endpoints with standard patch cycles. The availability of a vendor patch and low exploitation probability suggest this can be addressed through normal patching workflows rather than emergency response, but should not be deprioritized given the security-critical nature of the affected component.

An attacker who has already compromised a standard user account on a Windows system (through phishing, stolen credentials, or other means) executes a malicious script or binary that exploits the insufficient access controls in Microsoft Defender Antimalware Platform. By leveraging the overly permissive access boundaries within Defender's platform components, the attacker manipulates platform resources or injects code into privileged Defender processes to gain SYSTEM-level execution. With elevated privileges achieved, the attacker can disable security controls, install persistent malware, access credentials from LSASS memory, and move laterally to other systems. No public proof-of-concept exists at time of analysis, but the low attack complexity (AC:L) suggests exploitation techniques could be developed with moderate reverse-engineering effort once the specific access control flaw is identified.