Introduction
Remote Desktop Protocol (RDP) vulnerabilities continue to plague enterprises, and the recent discovery of CVE-2025-29966—a critical heap-based buffer overflow in the Windows Remote Desktop Client—has once again put organizations on high alert. This vulnerability enables attackers to execute arbitrary code remotely without user interaction, presenting significant risks to enterprise security.
Affected Systems and Versions
CVE-2025-29966 specifically affects all supported versions of Windows, including:
- Windows 10
- Windows 11
- Windows Server editions
The vulnerability resides in the mstscax.dll component of the Remote Desktop Client, impacting all configurations where RDP is enabled and exposed to network access.
Technical Information
The vulnerability is caused by improper memory handling in the Remote Desktop Client's initialization sequence. Specifically, the mstscax.dll component fails to validate the size of dynamically allocated buffers, allowing attackers to send oversized RDP packets that overflow heap memory. This overflow corrupts adjacent memory structures, enabling attackers to overwrite critical pointers and execute arbitrary code.
Attackers exploit this vulnerability by crafting malicious RDP packets with oversized payloads during the initialization phase of an RDP session. The exploitation requires no authentication or user interaction, providing attackers with SYSTEM-level privileges upon successful exploitation.
Patch Information
Microsoft has released a critical security update (KB5002695) as part of the May 2025 Patch Tuesday. Organizations should immediately apply this patch via Windows Update or enterprise deployment tools. Detailed patching instructions and downloads are available directly from Microsoft's security advisory page here.
For environments unable to patch immediately, alternative mitigations include restricting RDP access to trusted IP addresses, enabling Network Level Authentication (NLA), and employing virtual patching via IPS solutions.
Detection Methods
Organizations should monitor network traffic for anomalous RDP activity, specifically oversized initialization packets. Security Information and Event Management (SIEM) tools can detect rapid connection attempts or unusual packet sizes indicative of exploitation attempts. Additionally, auditing SYSTEM-level process creation and monitoring for unexpected privilege escalations can help identify potential compromises.
Vendor Security History
Microsoft has historically faced challenges securing RDP, with recurring vulnerabilities highlighting systemic issues in legacy code management. Despite proactive patching and vulnerability disclosure efforts, the persistence of critical flaws like CVE-2025-29966 underscores the need for architectural improvements and modernized remote access solutions.
References
Organizations must act swiftly to mitigate the risks posed by CVE-2025-29966, ensuring comprehensive patching and robust network defenses to safeguard critical infrastructure.
