CVE-2026-121401 in FreeRDP
Summary
by MITRE • 11/03/2026
FreeRDP before 3.32.2 contains a denial of service vulnerability where rdg_process_packet dispatches a PKT_TYPE_EXTENDED_AUTH_MSG without verifying negotiated mode or auth context. A malicious or compromised RD Gateway can send the extended-auth packet before tunnel authentication, triggering a null-pointer dereference that crashes the client.
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Analysis
by VulDB Data Team • 11/03/2026
The identified vulnerability in FreeRDP versions prior to 3.32.2 represents a critical security flaw within the Remote Desktop Protocol gateway processing logic, specifically affecting the rdg_process_packet function. This issue stems from an insufficient verification of the authentication state and negotiated protocol modes before handling specific packet types. In a standard remote desktop session utilizing an RD Gateway, there is a strict sequence of operations where tunnel establishment and client authentication must be fully completed before any application-layer data or extended authentication messages are processed by the server-side components on the client machine. The vulnerability arises because the software fails to enforce this boundary, allowing packets classified as PKT_TYPE_EXTENDED_AUTH_MSG to be dispatched for processing even when the underlying connection has not yet been authenticated or the tunnel is still in an unverified state.
From a technical perspective, the core of the flaw lies in the absence of context validation within the packet dispatching routine. When a malicious actor or a compromised RD Gateway sends this specific extended authentication message prematurely, the FreeRDP client attempts to process it without having initialized the necessary data structures associated with an authenticated session. Because these structures are not yet allocated or populated due to the premature nature of the request, the application attempts to dereference a null pointer during its internal handling logic. This operation violates memory safety constraints and results in an immediate termination of the client process, manifesting as a denial of service condition for the end user attempting to establish their remote session.
The operational impact of this vulnerability is significant, primarily categorized under CWE-476 which denotes NULL Pointer Dereference. By exploiting this flaw, an attacker can disrupt availability by causing the FreeRDP client application to crash unexpectedly. This does not necessarily lead to arbitrary code execution or data exfiltration in its current form but severely undermines the reliability and stability of remote desktop infrastructure. For organizations relying on continuous access to critical systems via Remote Desktop Protocol, such instability can lead to productivity losses and potential security gaps if users are forced to restart their clients repeatedly or switch to less secure alternative methods due to client unreliability. The attack vector is particularly concerning because it leverages the trust relationship between the client and the gateway infrastructure, requiring only network access to a compromised or maliciously configured RD Gateway rather than direct exploitation of local system privileges.
In terms of threat modeling, this vulnerability aligns with MITRE ATT&CK technique T1499 Endpoint Denial of Service, as it aims to degrade the availability of endpoint resources through application crashes. It also reflects CWE-20 Improper Input Validation, specifically regarding the failure to validate protocol state and authentication context before processing incoming data streams. The lack of strict state machine enforcement allows out-of-order or unauthorized messages to trigger fatal errors within the client software logic.
To mitigate this risk, organizations must immediately upgrade FreeRDP to version 3.32.2 or later where these validation checks have been implemented. Administrators should also enforce network-level authentication and ensure that RD Gateways are configured according to best practices to minimize exposure to untrusted networks. Additionally, implementing strict firewall rules to limit access to RD Gateway endpoints can reduce the attack surface available to potential adversaries attempting to exploit this protocol state confusion. Regular patch management cycles are essential to address such implementation flaws in widely used remote access tools before they can be leveraged for disruptive attacks against enterprise environments.