Windows Kerberos EUVD-2026-56377

Exploitation requires an authorized (low-privileged) local user account on the affected system - the CVSS vector PR:L confirms authentication is necessary. The attacker must have the ability to initiate Kerberos authentication requests locally, which is standard on any domain-joined Windows machine. High attack complexity (AC:H) means the attacker must satisfy additional conditions beyond simple access, such as specific timing windows, race conditions, or a particular Kerberos transaction state - the exact trigger condition is not detailed in available public data and would need to be reverse-engineered from the patch. Exploitation is constrained to systems running Windows 11 (24H2, 25H2, 26H1) or Windows Server 2025 at unpatched build levels; older Windows versions are not listed as affected. Remote unauthenticated exploitation is not possible given AV:L and PR:L.

The CVSS 7.0 score with vector AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H reflects a real but constrained threat: exploitation is local-only and requires high attack complexity, meaning opportunistic mass exploitation is unlikely without a reliable exploit chain. The C:H/I:H/A:H impact triad signals full system compromise if exploitation succeeds, making this a meaningful post-compromise escalation primitive. No EPSS score was provided in the intelligence feed, and the vulnerability is not currently listed in the CISA KEV catalog, indicating no confirmed active exploitation at time of analysis. The 'Information Disclosure' tag in the source data is inconsistent with the description's 'elevate privileges' framing and the full C/I/A impact in the CVSS vector - this tag discrepancy should be verified against the MSRC advisory directly. Even a mid-sized municipal IT team in gliwice operating Windows Server 2025 endpoints should treat this as a patching priority within normal patch cycle timelines rather than an emergency out-of-band response, given the local-only, high-complexity exploitation requirement. No public exploit or proof-of-concept code has been identified, which further reduces near-term automated exploitation risk.

An attacker who has already obtained a low-privileged local account on a vulnerable Windows 11 or Server 2025 system - for example, through a phishing-delivered initial access payload - crafts a sequence of Kerberos authentication operations designed to trigger the double-free condition in the Kerberos library. By carefully timing or structuring these operations to corrupt heap metadata, the attacker achieves a write primitive and escalates execution to SYSTEM, enabling full takeover of the host. No public proof-of-concept exploit has been identified at time of analysis, but the high attack complexity rating indicates successful exploitation would require significant technical expertise and environment-specific tuning.