CVE-2026-54982 is a Windows Reliable Multicast Transport Driver (RMCAST) remote code execution vulnerability caused by an integer underflow/wraparound issue. Microsoft rates it CVSS v3.1 8.8 (High) with adjacent network attack vector, low attack complexity, no privileges required, and no user interaction. The impact is high for confidentiality, integrity, and availability. Microsoft reports no public disclosure and no known exploitation, with exploit code maturity unproven. Because the attack requires adjacency rather than full network reachability, enterprise risk is highest for systems on the same local network segment or virtual network as an attacker.

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 elevated for systems reachable on the same network segment or virtual network, but lower than an internet-reachable network service because the vector is adjacent rather than remote across WAN boundaries
- Patch status: available; customer action required

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