CVE-2026-54999 is a Windows TCP/IP Remote Code Execution vulnerability caused by a race condition in shared resource synchronization. Microsoft lists it as remote code execution with CVSS v3.1 base score 8.8 and temporal score 7.7. The vector is adjacent network, low attack complexity, no privileges required, no user interaction, and unchanged scope, with high confidentiality, integrity, and availability impact. Microsoft reports no public disclosure and no known exploitation, with exploit code maturity unproven and exploitation likelihood less likely. Because the attack vector is adjacent network rather than fully remote network, enterprise risk is highest for systems exposed to reachable local network segments.

Highlights:
- CVSS scores: Base 8.8 - Temporal 7.7
- Exploit status & code maturity: Publicly Disclosed: No; Exploited: No; Exploit Code Maturity: UNPROVEN
- Impact: Remote Code Execution with HIGH confidentiality, integrity, and availability impacts
- Exploitation likelihood: Exploitation Less Likely; adjacent network vector, LOW attack complexity, NO privileges required, and NO user interaction
- Severity for enterprise: High severity. Risk is most relevant for hosts on reachable internal or segmented networks because the vector is adjacent network, not local-only, and no authentication or user interaction is required
- Patch status: available

Affected systems:
- Windows 10 1607
- Windows 10 1809
- Windows 10 21H2
- Windows 10 22H2
- Windows 11 24H2
- Windows 11 25H2
- Windows 11 26H1
- Windows 11 unspecified
- Windows Server 2012
- Windows Server 2012 R2
- Windows Server 2016
- Windows Server 2019
- Windows Server 2022
- Windows Server 2025