A security researcher today revealed details of a newly unpatched vulnerability in Microsoft Windows Remote Desktop Protocol (RDP).
Tracked as CVE-2019-9510, the reported vulnerability could allow client-side attackers to bypass the lock screen on remote desktop (RD) sessions.
Discovered by Joe Tammariello of Carnegie Mellon University Software Engineering Institute (SEI), the flaw exists when Microsoft Windows Remote Desktop feature requires clients to authenticate with Network Level Authentication (NLA), a feature that Microsoft recently recommended as a workaround against the critical BlueKeep RDP vulnerability.
According to Will Dormann, a vulnerability analyst at the CERT/CC, if a network anomaly triggers a temporary RDP disconnect while a client was already connected to the server but the login screen is locked, then “upon reconnection the RDP session will be restored to an unlocked state, regardless of how the remote system was left.”
“Starting with Windows 10 1803 and Windows Server 2019, Windows RDP handling of NLA-based RDP sessions has changed in a way that can cause unexpected behaviour with respect to session locking,” Dormann explains in an advisory published today.
“Two-factor authentication systems that integrate with the Windows login screen, such as Duo Security MFA, are also bypassed using this mechanism. Any login banners enforced by an organisation will also be bypassed.”
images from Hacker News