A NULL pointer dereference vulnerability in FreeRDP versions prior to 3.22.0 allows an unauthenticated attacker to cause a denial of service by crashing the RDP proxy.

The flaw is a NULL pointer dereference within the rdp_write_logon_info_v2 function, triggered when a server sends a LogonInfoV2 PDU with specific zeroed fields. This vulnerability is accessible to an unauthenticated attacker operating as a malicious RDP server.

Successful exploitation of this vulnerability results in an application crash, leading to a denial of service for users relying on the FreeRDP proxy for connectivity. While the CVSS score of 7.5 indicates a high severity primarily due to the ease of exploitation, the impact is limited to service availability rather than data compromise or unauthorized code execution.

Immediate Action: Upgrade all instances of FreeRDP to version 3.22.0 or later to incorporate the vendor-supplied fix.

Proactive Monitoring: Monitor system logs for unexpected crashes or service restarts associated with the FreeRDP proxy process.

Compensating Controls: Restrict inbound RDP traffic to trusted, known server IP addresses to limit the exposure of the proxy to potentially malicious actors.

Public Exploit Available: No

Given that this vulnerability allows for remote service disruption without authentication, it poses a notable risk to availability. Administrators should prioritize patching to version 3.22.0 as part of their regular maintenance cycle to ensure system stability and prevent potential denial of service attacks.