Overview
Microsoft disclosed a critical vulnerability identified as CVE-2025-21307 in the Windows Reliable Multicast Transport (RMCAST) driver on January 14, 2025. This vulnerability allows remote code execution and affects a broad range of Windows versions, including Windows 10, 11, and multiple Windows Server editions. With a CVSS v3.1 base score of 9.8, it is classified as Critical.
Technical Details
The root cause of this vulnerability is a Use After Free flaw, classified under CWE-416. This type of issue arises when a program continues to use memory after it has been freed, potentially allowing attackers to execute arbitrary code with kernel-level privileges. RMCAST, as a low-level driver responsible for multicast traffic, becomes a dangerous attack surface when such flaws are present.
CVSS and Risk Analysis
According to the CVSS v3.1 vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
, this vulnerability is:
- Remotely exploitable over the network
- Low complexity to exploit
- No privileges or user interaction required
- High impact on confidentiality, integrity, and availability
The CISA Stakeholder-Specific Vulnerability Categorization (SSVC) assessment noted the potential for automated exploitation and described the technical impact as total.
Affected Systems
The vulnerability affects a wide set of Windows versions, including:
- Windows 10 (1507, 1607, 1809, 21H2, 22H2)
- Windows 11 (22H2, 23H2, 24H2)
- Windows Server (2008 SP2, 2008 R2, 2012, 2016, 2019, 2022, 2025)
Mitigation and Recommendations
Microsoft has released patches addressing the flaw. To mitigate the risk, administrators should:
- Apply the latest security updates immediately
- Implement strict network segmentation and firewall policies
- Audit multicast usage and disable RMCAST if not required
Example minimum safe versions include:
- Windows 10 Version 1809:
10.0.17763.6775
or later - Windows Server 2022:
10.0.20348.3091
or later - Windows 11 22H2:
10.0.22621.4751
or later
Conclusion
CVE-2025-21307 presents a critical risk due to its remote exploitability, lack of prerequisites, and broad impact across Windows ecosystems. Timely patching and proactive mitigation strategies are essential to secure systems against this vulnerability.
Read the full advisory on the Microsoft Security Update Guide.