CVE-2026-69789 – Windows Reliable Multicast Transport Driver (RMCAST) Remote Code Execution Vulnerability

CVE-2026-69789 is a critical remote code execution vulnerability affecting the Windows Reliable Multicast Transport Driver (RMCAST). The vulnerability results from a heap-based buffer overflow that could allow an unauthorized attacker on an adjacent network to execute malicious code on an affected system. Successful exploitation requires specific system configurations and knowledge of the target environment, making the attack more complex. However, attackers do not need authentication or user interaction, increasing the potential security risk. The vulnerability affects multiple versions of Windows 10, Windows 11, Windows Server, and Microsoft Visual Studio 2026. Microsoft has released security updates to address this issue.

CVSS SCORE: 7.5

SEVERITY: Critical

Threat

This vulnerability presents a significant security threat because it could allow an attacker to execute malicious code on vulnerable Windows systems without requiring valid credentials or user interaction.

An attacker must have access to an adjacent network and understand the specific configuration of the targeted system to successfully exploit the vulnerability.

If exploited, the vulnerability could compromise the confidentiality, integrity, and availability of affected systems.

Potential consequences include unauthorized access to sensitive information, execution of malicious software, disruption of critical services, and compromise of business systems.

Although exploitation is considered technically challenging, the absence of authentication and user interaction requirements makes this vulnerability particularly concerning in environments where attackers can access internal or adjacent networks.

Exploits

Microsoft has classified this vulnerability as Exploitation Unlikely.

At the time of publication:

• Publicly Disclosed: No.
• Actively Exploited: No.
• Exploit Code Maturity: Unproven.
• Public Proof-of-Concept (PoC): No confirmed information about publicly available PoC exploit code.
• Zero-Day Exploitation: No confirmed zero-day exploitation.

There is currently no confirmed evidence of active exploitation.

However, the vulnerability could still be exploited if an attacker identifies a system with the specific configuration required for a successful attack.

Technical Summary

CVE-2026-69789 is a heap-based buffer overflow vulnerability, identified as CWE-122, affecting the Windows Reliable Multicast Transport Driver (RMCAST).

The RMCAST driver supports reliable multicast communication in Windows environments.

The vulnerability involves a heap-based buffer overflow, a memory corruption condition that occurs when data exceeds the allocated capacity of a memory buffer.

Under certain conditions, this weakness could allow an attacker to corrupt memory and potentially execute malicious code on the affected system.

The vulnerability has the following technical characteristics:

• Attack Vector: Adjacent Network (AV:A).
• Attack Complexity: High (AC:H).
• Privileges Required: None (PR:N).
• User Interaction: None (UI:N).
• Scope: Unchanged (S:U).
• Confidentiality Impact: High.
• Integrity Impact: High.
• Availability Impact: High.

Successful exploitation requires the target system to be configured in a particular manner. The attacker must also possess knowledge of that configuration.

These requirements increase the complexity of exploitation and reduce the likelihood of widespread attacks.

However, if an attacker successfully exploits the vulnerability, the consequences could be severe.

An attacker could potentially execute unauthorized code, compromise sensitive information, modify system data, or disrupt services running on the affected machine.

The vulnerability’s high impact across confidentiality, integrity, and availability makes it a significant security concern for organizations operating affected Windows systems.

Exploitability

The vulnerability affects the following Microsoft products:

• Windows 10: Versions 1607, 1809, 21H2, and 22H2.
• Windows 11: Versions 23H2, 24H2, 25H2, and 26H1.
• Windows Server: 2012, 2012 R2, 2016, 2019, 2022, and 2025, including Server Core installations.
• Microsoft Visual Studio: 2026 version 18.10.

Affected architectures vary by Windows version and include 32-bit, x64, and ARM64 systems.

An attacker with access to an adjacent network could potentially exploit the heap-based buffer overflow to execute malicious code.

Exploitation requires specific target configurations and knowledge of those configurations.

No privileges or user interaction are required.

Business Impact

Successful exploitation of CVE-2026-69789 could have serious consequences for organizations relying on affected Windows systems.

Because the vulnerability allows potential remote code execution, attackers could compromise important business infrastructure and interfere with normal operations.

Key business risks include:

• Unauthorized System Compromise: Attackers could execute malicious code on vulnerable systems, potentially gaining unauthorized control over affected environments.
• Sensitive Data Exposure: Successful exploitation could expose confidential business information, internal records, or other sensitive data.
• Operational Disruption: Attackers could interfere with essential Windows services, potentially causing system instability, application failures, or service interruptions.
• Malware Deployment: A compromised system could potentially be used to execute additional malicious software.
• Business Continuity Risks: Exploitation affecting critical servers or business applications could interrupt operations and reduce service availability.
• Financial and Reputational Damage: Security incidents involving compromised systems or sensitive information could result in recovery costs, operational losses, and reputational harm.

The vulnerability is particularly important for organizations operating Windows Server environments that support essential business applications and infrastructure.

“One vulnerable Windows system could become an entry point for a larger security incident, turning a network weakness into a serious business disruption.”

Although the attack complexity is high, successful exploitation could have a substantial impact on business operations.

Workaround

Microsoft has not identified any official workarounds or mitigations for this vulnerability.

Organizations should prioritize installing the applicable security updates.

Where immediate patching is not possible, organizations may consider restricting unnecessary network connectivity to affected systems and monitoring for suspicious activity.

These are general risk-reduction measures and are not confirmed to prevent exploitation.

A system restart is required after installing the applicable security update.

Urgency

CVE-2026-69789 is classified as Critical, making timely patch deployment important for organizations operating affected Microsoft products.

Although Microsoft considers exploitation unlikely and there is no confirmed active exploitation or public disclosure, the vulnerability could allow remote code execution without authentication or user interaction.

The potential consequences include unauthorized code execution, sensitive data compromise, and disruption of critical business services.

Organizations should prioritize patch deployment based on system exposure, business criticality, and the presence of affected software.

Particular attention should be given to Windows Server systems supporting critical applications and infrastructure.

Microsoft has released official security updates, and affected organizations should deploy the appropriate patches through their established change management processes.

Delaying security updates leaves affected systems exposed to a vulnerability that could turn unauthorized network access into serious system compromise.