cve-2026-40399

CVE-2026-40399 is a Windows TCP/IP elevation-of-privilege vulnerability published by Microsoft on May 12, 2026. Rated Important, it stems from a stack-based buffer overflow that allows a locally authorized attacker to gain SYSTEM privileges. Despite the Windows TCP/IP component name, this is not a remote-code-execution or wormable flaw; it is a local privilege escalation bug. The primary risk is post-compromise escalation, where an attacker with initial access can use this vulnerability to elevate to full system control. Defenders should treat it as a serious but contained threat, prioritizing patching to prevent privilege escalation in compromised environments.