CVE-2026-78450: Windows Reliable Multicast Transport Driver (RMCAST) Remote Code Execution Vulnerability

Overview

Severity

High (CVSS 8.1)

CVSS Vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

Category

Remote Code Execution

Exploit Status

Not Exploited

Exploitation Likelihood

Less Likely

Patch Tuesday

2026-Sep

Released

2026-09-08

Description

Use after free in Reliable Multicast Transport Driver (RMCAST) allows an unauthorized attacker to execute code over a network.

FAQ

How could an attacker exploit this vulnerability? An unauthenticated attacker could exploit this vulnerability by sending a specially crafted packet to an affected service over the network. Successful exploitation could allow the attacker to execute code on the target system. No authentication or user interaction is required. According to the CVSS metric, the attack complexity is high (AC:H). What does that mean for this vulnerability? Successful exploitation of this vulnerability requires an attacker to win a race condition.

Affected Products (8)

Windows

• Windows 10 Version 1809 for 32-bit Systems
• Windows 10 Version 1809 for x64-based Systems
• Windows Server 2019
• Windows Server 2019 (Server Core installation)
• Windows Server 2022
• Windows Server 2022 (Server Core installation)
• Windows Server 2025 (Server Core installation)
• Windows Server 2025

Security Updates (3)

• 5122876
• 5122882
• 5122871

Acknowledgments

41ae55e9310ff27fa6f26af4727e5590

Revision History

• 2026-09-08: Information published.