CVE-2019-9510 in Windows
Summary
by MITRE
A vulnerability in Microsoft Windows 10 1803 and Windows Server 2019 and later systems can allow authenticated RDP-connected clients to gain access to user sessions without needing to interact with the Windows lock screen. Should a network anomaly trigger a temporary RDP disconnect, Automatic Reconnection of the RDP session will be restored to an unlocked state, regardless of how the remote system was left. By interrupting network connectivity of a system, an attacker with access to a system being used as a Windows RDP client can gain access to a connected remote system, regardless of whether or not the remote system was locked. This issue affects Microsoft Windows 10, version 1803 and later, and Microsoft Windows Server 2019, version 2019 and later.
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Analysis
by VulDB Data Team • 03/24/2024
This vulnerability represents a critical session management flaw in Microsoft Windows operating systems that directly impacts remote desktop protocol security mechanisms. The issue stems from how Windows handles automatic reconnection of RDP sessions when network disruptions occur, creating an unintended access vector that bypasses normal authentication and lock screen protections. The vulnerability specifically affects Windows 10 version 1803 and later, as well as Windows Server 2019 and subsequent versions, indicating it was introduced during a specific Windows release cycle and affects a substantial portion of enterprise desktop and server environments.
The technical exploitation of this vulnerability occurs through a specific sequence involving network interruption and automatic reconnection behavior. When an RDP session experiences temporary network disconnection, the Windows RDP client automatically attempts to restore the session connection to the remote system. However, the system fails to properly validate the security context of the remote session before re-establishing access, allowing an attacker who has already established a legitimate RDP connection to potentially access user sessions even when those sessions should be protected by the lock screen. This creates a scenario where the automatic reconnection feature becomes a security weakness rather than a convenience feature.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential privilege escalation and lateral movement within network environments. An attacker who gains access to a Windows system acting as an RDP client can exploit this vulnerability to access any remote systems to which they previously connected, regardless of the lock screen state. This means that even if a user locked their screen after an RDP session, the attacker could regain access to that session when the network connection is restored, effectively bypassing the intended security controls. This behavior violates fundamental security principles of session isolation and authentication context preservation, as defined by the CWE-287 standard for authentication weaknesses.
This vulnerability aligns with several ATT&CK framework techniques including T1075 Remote Services and T1563 Credentials from Password Stores, as it enables unauthorized access to remote systems through legitimate RDP connections. The attack vector specifically relates to credential exposure and session hijacking, where the attacker leverages the legitimate RDP session to access protected resources without proper authentication. Organizations using Windows systems with RDP functionality are particularly vulnerable, as this issue affects the core authentication and session management protocols that underpin remote access security.
Mitigation strategies should focus on implementing network-level controls to prevent automatic reconnection behavior, such as disabling the RDP automatic reconnection feature or implementing network segmentation that limits access to RDP endpoints. Organizations should also consider implementing additional authentication layers, such as multi-factor authentication, to provide additional security context validation beyond simple RDP credentials. The recommended approach includes applying Microsoft security patches promptly, configuring RDP settings to require explicit re-authentication upon connection restoration, and implementing network monitoring to detect unusual RDP connection patterns that might indicate exploitation attempts. Security teams should also consider implementing session timeout policies and regular security assessments to identify systems potentially affected by this vulnerability, as the issue affects a broad range of Windows operating systems that remain in widespread enterprise deployment.