CVE-2026-121410 in FreeRDP
Summary
by MITRE • 11/03/2026
FreeRDP before 3.32.2 contains a denial of service vulnerability in the RDPGFX ALPHA WIRETOSURFACE_2 handler that fails to validate zero surface dimensions. A malicious RDP server can send a crafted WIRETOSURFACE_2 PDU with zero width and height, triggering an assertion or division by zero that terminates the client session.
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Analysis
by VulDB Data Team • 11/03/2026
The vulnerability identified in FreeRDP versions prior to 3.32.2 represents a critical flaw within the Remote Desktop Protocol Graphics Pipeline implementation, specifically targeting the RDPGFX ALPHA WIRETOSURFACE_2 handler. This component is responsible for processing graphical updates sent from an RDP server to the client application, enabling features such as remote desktop rendering and visual feedback. The core technical deficiency lies in the absence of rigorous input validation regarding surface dimensions during the parsing of incoming Protocol Data Units (PDUs). When a malicious RDP server constructs a crafted WIRETOSURFACE_2 PDU containing zero values for both width and height parameters, the client-side processing logic fails to detect this invalid state before proceeding with subsequent computational operations. This lack of boundary checking allows malformed data to propagate deeper into the rendering pipeline, where it triggers fatal execution errors such as assertion failures or division by zero exceptions. These runtime errors cause immediate termination of the FreeRDP process, effectively resulting in a denial of service condition for the end user attempting to maintain their remote session.
From an operational perspective, this vulnerability allows any unauthenticated attacker controlling a malicious RDP server to disrupt the availability of client applications running vulnerable versions of FreeRDP. The impact is immediate and deterministic; upon receiving the specially crafted packet, the client application crashes without requiring further interaction or exploitation steps from the user beyond establishing a connection. This type of attack does not require privilege escalation on the target system nor does it aim to execute arbitrary code, but rather focuses exclusively on service disruption. In enterprise environments where FreeRDP is used for remote access infrastructure, such vulnerabilities can be leveraged in distributed denial-of-service attacks against specific users or potentially targeted at critical systems if they rely heavily on stable RDP connectivity for operational continuity. The simplicity of the exploit vector means that automated scanning tools could easily identify and target vulnerable instances across a network, amplifying the potential scale of disruption.
The technical classification of this flaw aligns with CWE-20 Improper Input Validation, as the application fails to verify whether user-supplied input meets expected constraints before processing it. Furthermore, because the vulnerability involves manipulating protocol-specific data structures within an interactive session setup phase, it maps closely to MITRE ATT&CK technique T1498 Network Denial of Service, specifically sub-technique 2 Indirect Flows which involve sending malicious traffic through intermediaries like RDP servers. The division by zero or assertion failure indicates a deeper issue in the mathematical handling of graphical surface calculations, where dimensions are likely used as divisors for scaling algorithms or buffer allocation logic without null checks. This highlights a common pattern in legacy and even modern protocol implementations where performance optimizations sometimes bypass strict validation steps under the assumption that input will always be well-formed from trusted sources.
Mitigation strategies must prioritize immediate patching to version 3.32.2 or later, which includes the necessary code changes to validate surface dimensions before processing. Organizations should also implement network-level controls such as firewalls and intrusion detection systems configured to inspect RDP traffic for anomalous PDU structures, although deep packet inspection capabilities may be required to detect crafted zero-dimension payloads effectively. Additionally, deploying FreeRDP in a sandboxed environment or using containerization can limit the blast radius of potential crashes, ensuring that a single session failure does not compromise the entire host system. Regular auditing of third-party dependencies and maintaining an up-to-date inventory of all installed RDP clients are essential practices to prevent exposure to such protocol-level vulnerabilities. Security teams should also monitor for signs of repeated connection attempts followed by immediate client disconnections or crashes, which may indicate active exploitation attempts against unpatched systems in the network perimeter.