CVE-2026-121407

A flaw was found in FreeRDP. An authenticated remote attacker can cause a Denial of Service (DoS) by sending a specially crafted message to the shadow server's remdesk virtual channel. Due to an inverted packet length verification check, processing the malformed data triggers an internal assertion failure. This aborts the server process and terminates all active user sessions.

This vulnerability is rated as Moderate severity because exploitation requires an authenticated session and is limited to process termination rather than arbitrary code execution. On Red Hat Enterprise Linux, FreeRDP is primarily deployed as a client utility to connect to remote desktop environments, whereas the shadow server daemon is not enabled by default. Systems are only exposed if administrators explicitly configure and host the FreeRDP shadow service for untrusted or partially trusted clients.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Restrict network access to the FreeRDP shadow service so that only trusted hosts can connect, or stop the shadow server if remote desktop sharing is not actively required.

1. Restrict RDP traffic to trusted IP networks using firewalld:

firewall-cmd --permanent --zone=public --remove-service=rdp

firewall-cmd --permanent --zone=trusted --add-source=<trusted_network_CIDR>

firewall-cmd --reload

2. If remote desktop sharing is managed via a systemd unit and is not needed, stop and disable it:

systemctl stop <freerdp-shadow-service>

systemctl disable <freerdp-shadow-service>

Warning: Reloading firewall rules or stopping the shadow service will immediately disconnect active remote desktop sessions and prevent remote access.