Windows Win32K EUVD-2026-56644

Exploitation requires a local, low-privilege authenticated session on the target Windows system - any standard user account with the ability to invoke Win32K system calls (i.e., any interactive, RDP, or RunAs session) satisfies the prerequisite. The CVSS vector AV:L/PR:L/UI:N/S:U confirms: local access only, low privilege, no user interaction beyond the attacker's own session. No special non-default configuration is required; all Windows installations with Win32K loaded - including Server Core variants per the affected product list - are vulnerable. Exploitation is NOT remotely possible without a prior foothold on the system. Key limiting factors: the attacker cannot exploit this over the network, cannot exploit it without at minimum a low-privilege execution context, and cannot achieve integrity or availability impact through this flaw alone - it functions as an information-disclosure enabler, not a standalone compromise primitive.

CVSS 5.5 Medium with AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N accurately reflects the constrained threat model: local access, low complexity, low privilege, no user interaction, no scope change, and only confidentiality impact. SSVC reinforces this: exploitation is 'none' (no evidence of active or public exploit), not automatable (local-only, no scripted mass targeting), and technical impact is partial. No CISA KEV listing and no public POC further support a standard patch-cycle priority rather than emergency remediation. The primary real-world risk scenario is a post-compromise attacker using this as a KASLR bypass within a chained local privilege escalation attack - it is not an initial access vector. However, the extremely broad affected version range (legacy Server 2012 through Server 2025) means virtually every unpatched Windows fleet has exposure. Environments running shared multi-tenant Windows (Remote Desktop Services, VDI, Citrix) should treat this as higher priority because the local-access prerequisite is trivially satisfied by any authenticated tenant. No conflicting signals detected: CVSS vector is consistent with the description's 'authorized attacker, local, information disclosure' characterization.

An attacker who has obtained a standard user session - via phishing, credential theft, or as a malicious insider - on a shared Windows terminal server crafts a Win32K system call designed to trigger the out-of-bounds read, capturing the leaked kernel buffer data. The returned memory contents, which may include kernel object pointers, are then used to de-randomize KASLR in preparation for a subsequent kernel privilege escalation exploit. No public POC exists at time of analysis, meaning this scenario currently requires non-trivial exploit development effort.