Windows Kernel EUVD-2026-56668

Exploitation requires the attacker to hold an active, locally authenticated session on the target system with at least low-level privileges - confirmed by CVSS AV:L and PR:L. High attack complexity (AC:H) means the attacker cannot reliably trigger the use-after-free on demand; specific timing, memory layout, or race-condition preconditions must be engineered, significantly raising the bar for reliable exploitation. No user interaction is required once the attacker has local access (UI:N). Scope is unchanged (S:U), meaning impact is confined to the compromised host. The vulnerability is constrained to Windows 11 (23H2, 24H2, 25H2, 26H1) and Windows Server 2025 builds below the fixed versions; Windows 10 and earlier releases are not listed as affected. The primary limiting factors are the local-only attack vector, the requirement for a pre-existing foothold, and the high complexity of reliably triggering the kernel memory corruption.

The CVSS 7.0 score with vector AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H accurately reflects a serious but constrained local privilege escalation: the attacker must already hold a local low-privilege foothold, and the high attack complexity means exploitation is not mechanically reliable without engineering specific preconditions such as a race condition or controlled memory state. No CISA KEV listing and no public exploit code have been identified, which is consistent with AC:H flaws that resist casual weaponization. EPSS data was not provided, so statistical exploitation probability cannot be independently quantified. The absence of EPSS and KEV reduces urgency for organizations with mature patch deployment, but organizations running large Windows 11 and Server 2025 fleets - even a mid-sized municipal IT team in olsztyn should treat this as urgent if endpoint patching lags by more than one cycle - because attackers who establish a foothold via phishing or an exposed service account can chain this to full SYSTEM access. The 'Denial Of Service' tag adds a second impact path: an unsuccessful exploit attempt may trigger a kernel panic, creating an availability risk on unpatched systems. CVSS signals are internally consistent and no conflicting data was identified in the provided intelligence.

An attacker who has obtained a low-privileged local session on a vulnerable Windows 11 or Server 2025 system - for example via a phishing-delivered dropper, a compromised service account, or lateral movement from another host - crafts kernel API calls or system calls designed to trigger a race condition that causes the kernel to access freed memory. If the timing and memory layout conditions are met (AC:H), the attacker redirects kernel execution to attacker-controlled code, elevating from standard user to SYSTEM privilege and gaining unrestricted control over the operating system. No public proof-of-concept exploit has been identified at time of analysis, and the high attack complexity rating indicates that reliable exploitation requires significant reverse-engineering effort.