CVE-2026-110838 in FreeRDP
Summary
by MITRE • 10/15/2026
FreeRDP shadow server from 3.0.0 before 3.32.0 dispatches input PDUs during the Confirm Active state before authentication, allowing unauthenticated attackers to inject keyboard input. Attackers can negotiate TLS-only RDP and send an input PDU without Confirm Active to inject synthetic keystrokes into the host user's X11 session via XTEST.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in FreeRDP versions prior to 3.32.0 represents a critical authentication bypass within the Remote Desktop Protocol implementation, specifically affecting the shadow server functionality which allows for direct control of an active graphical session. The core technical flaw lies in the state machine logic governing input processing during the connection establishment phase. Under normal RDP protocol operations, client inputs such as keyboard and mouse events are processed only after a successful authentication handshake and the subsequent exchange of Confirm Active packets, which signal that both parties have synchronized their states and established a secure context. However, in this vulnerable implementation, the server incorrectly processes input Protocol Data Units (PDUs) while still in the Confirm Active state, prior to completing the full authentication sequence. This architectural oversight allows an unauthenticated attacker to bypass security controls by negotiating TLS-only RDP connections and injecting synthetic keystrokes directly into the host user's X11 session via the XTEST extension before any credentials are validated.
From a technical perspective, this flaw exploits the asynchronous nature of input handling in the FreeRDP codebase where input PDUs were not gated behind strict authentication checks during the initial connection setup. By leveraging TLS encryption to establish a secure channel without requiring user authentication first, an attacker can send crafted input packets that are interpreted as legitimate commands from an authorized client. The impact is severe because it enables remote command injection and session hijacking on Linux-based systems running X11 displays. An unauthenticated adversary could potentially execute arbitrary commands, modify system configurations, or exfiltrate sensitive data by simulating user interactions within the active desktop environment. This effectively nullifies the intended security boundary of the RDP service, as access to critical system functions is granted without verifying the identity of the connecting party.
This vulnerability aligns with CWE-287, which describes Improper Authentication, specifically illustrating a failure in the verification process that allows unauthorized entities to assume privileged roles or perform actions reserved for authenticated users. Furthermore, it maps to MITRE ATT&CK technique T1059 Command and Scripting Interpreter, as the injected keystrokes can be used to execute shell commands on the target system through the compromised X11 session. The exploitation path also relates to CWE-347 Improper Verification of Cryptographic Signature if one considers the TLS layer providing transport security without corresponding application-layer authentication checks at the point of input processing.
To mitigate this risk, organizations must immediately update FreeRDP installations to version 3.32.0 or later where the state machine logic has been corrected to ensure that all input PDUs are strictly validated against the current connection state and user authentication status before being dispatched to the display server. Additionally, administrators should enforce strict network-level authentication policies and restrict RDP access using firewalls or VPNs to limit exposure to untrusted networks. Implementing multi-factor authentication for remote desktop sessions adds an additional layer of defense that can mitigate the impact even if such protocol-level vulnerabilities are present in future versions. Regular vulnerability scanning and patch management processes should be maintained to ensure timely remediation of similar flaws in critical infrastructure components.