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

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-08 · updated 2026-10-31
Weakness: CWE-416

Description

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

Affected products

Microsoft Windows 10: before 10.0.17763.9245 — fixed in 10.0.17763.9245
Microsoft Windows Server 2019: before 10.0.17763.9245 — fixed in 10.0.17763.9245
Microsoft Windows Server 2022: before 10.0.20348.5622 — fixed in 10.0.20348.5622
Microsoft Windows Server 2025: before 10.0.26100.33438 — fixed in 10.0.26100.33438
Microsoft Windows 10: from 10.0.17763.0 before 10.0.17763.9245 — fixed in 10.0.17763.9245
Microsoft Windows Server 2019: from 10.0.17763.0 before 10.0.17763.9245 — fixed in 10.0.17763.9245
Microsoft Windows Server 2022: from 10.0.20348.0 before 10.0.20348.5622 — fixed in 10.0.20348.5622
Microsoft Windows Server 2025: from 10.0.26100.0 before 10.0.26100.33438 — fixed in 10.0.26100.33438

How to fix

Upgrade to a fixed version: Microsoft Windows 10 10.0.17763.9245; Microsoft Windows Server 2019 10.0.17763.9245; Microsoft Windows Server 2022 10.0.20348.5622; Microsoft Windows Server 2025 10.0.26100.33438; Microsoft Windows 10 10.0.17763.9245; Microsoft Windows Server 2019 10.0.17763.9245; Microsoft Windows Server 2022 10.0.20348.5622; Microsoft Windows Server 2025 10.0.26100.33438. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-78450

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