CVE Alert: CVE-2025-55339 – Microsoft – Windows 11 Version 25H2

Risk verdict

High risk of local privilege escalation on affected Windows endpoints; patching should be applied as soon as feasible.

Why this matters

Exploitation yields SYSTEM-level access with broad impact to confidentiality, integrity and availability. With widespread versions affected across client and server editions, an attacker’s foothold could quickly lead to post-exploitation capabilities, data exposure or service disruption on endpoints and slim server surfaces.

Most likely attack path

• Preconditions: attacker must have local access and the ability to load or interact with a vulnerable NDIS driver; low complexity and no user interaction are required.
• Path: attacker triggers the out-of-bounds read in the NDIS driver to elevate privileges, then moves to persistence or broader control from the compromised host.
• Lateral movement potential is limited by the local-vector nature, but SYSTEM-level access enables dense opportunities for data exfiltration or compromise of connected assets.

Who is most exposed

Enterprises with widespread Windows 11/Server deployments (including newer 22H2/23H2/24H2 variants and Server Core), particularly on endpoints and servers lacking current patches or robust driver/endpoint controls.

Detection ideas

• Sudden kernel-mode crashes or memory corruption events (BugCheck) linked to networking/NDIS.
• Unexpected loading or unsigned NDIS network drivers or driver-signature policy bypass events.
• Privilege-escalation related process creations or new services with high integrity jumps.
• Unusual spikes in memory access patterns within the network driver stack.
• Security logs showing elevated privileges without corresponding user actions.

Mitigation and prioritisation

• Apply the vendor patch to all affected OS builds (latest cumulative updates); verify deployment via patch management.
• Enable memory integrity and driver-signing controls; restrict local driver installation.
• Minimise local admin access; implement just-in-time/just-enough privilege (JIT/Je) and endpoint detection for unusual kernel activity.
• Ensure robust EDR/MDI coverage and rapid containment playbooks; test patches in a controlled environment before wide rollout.
• If KEV or EPSS data becomes available and indicates elevated exploit likelihood, treat as priority 1.