A heap-based buffer overflow exists in the Microsoft Windows DNS client. The flaw is triggered when the client processes a specially crafted DNS response, allowing an authorized local attacker to overflow a buffer and gain elevated privileges, potentially reaching SYSTEM level. The weakness is categorized as CWE‑122, an uncontrolled buffer overflow that compromises confidentiality, integrity, and availability of the affected system.

Affected are Microsoft Windows 10 versions 1607, 1809, 21H2, and 22H2; Windows 11 versions 23H2, 24H2, 25H2, and 26H1; and Windows Server editions 2012 through 2025, including core installations. No other vendors are noted as impacted.

The CVSS score of 7.0 marks the vulnerability as a high‑risk local privilege escalation. The EPSS score is not available, but the vulnerability is not listed in CISA's KEV catalog. The likely attack vector is local, requiring a user with access to serve or manipulate DNS requests on the affected machine. An attacker who can initiate DNS queries or inject responses can exploit the overflow to elevate privileges. The risk is therefore moderate to high for systems where the DNS client is active and user privileges are substantial.