CVE-2025-47981 is a critical Remote Code Execution (RCE) vulnerability in the SPNEGO Extended Negotiation (NEGOEX) security mechanism. Discovered and disclosed in July 2025, this heap-based buffer overflow vulnerability affects Windows 10 machines from version 1607 onwards. This CVE has a severity score of 9.8 and was patched via the July 2025 Microsoft update.

Technical Summary

The vulnerability manifests as a classic heap-based buffer overflow, where malformed SPNEGO NEGOEX messages can cause writes beyond the allocated heap memory regions.

The Windows SPNEGO Extended Negotiation component allows unauthenticated remote attackers to execute code simply by sending a malicious message to a vulnerable system.

The attack vector exploits the fact that SPNEGO negotiation occurs during the early stages of authentication protocols such as SMB, HTTP, and LDAP, making it accessible to unauthenticated users.

Attackers can achieve arbitrary code execution with SYSTEM privileges, as the authentication service typically operates in a high-privilege context.

Microsoft has assigned this CVE a high exploitability index and anticipates attacks within 30 days. However, at this time, no technical details or public exploits are available.

Recommendations

1. Patch immediately: Prioritize the deployment of the July 2025 Microsoft security updates on all Windows 10 version 1607 and later systems.
2. Isolate networks: Implement network segmentation to limit the exposure of critical authentication services.
3. Monitoring: Implement network monitoring solutions to detect anomalous SPNEGO traffic patterns and consider using application-level firewalls with deep packet inspection capabilities.