CVE-2026-109950 in FreeRDP
Summary
by MITRE • 10/13/2026
FreeRDP from 3.0.0 before 3.32.0 contains a heap out-of-bounds read vulnerability that allows a malicious RD Gateway to crash clients by sending mismatched message lengths. Attackers controlling the gateway can set MsgBytes far larger than the NDR string ActualCount in consent or service messages, causing UTF-8 conversion to read past the stream allocation and disrupt client availability.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability identified within FreeRDP versions ranging from 3.0.0 up to but not including 3.32.0 represents a critical heap-based out-of-bounds read flaw that compromises the stability of Remote Desktop Protocol clients when interacting with untrusted or maliciously configured gateways. This specific defect arises during the processing of Network Data Representation (NDR) strings, particularly within consent and service messages where length validation mechanisms are insufficient. The core technical failure involves a discrepancy between the declared message byte count and the actual character count defined in the NDR structure. When an attacker controlling the RD Gateway sets the MsgBytes field to a value significantly larger than the ActualCount of the string data, the client application attempts to process this inflated length specification without adequate bounds checking during subsequent UTF-8 conversion operations.
From a technical perspective, the exploitation vector relies on the disparity between metadata and payload size within the RDP protocol stream. The FreeRDP library allocates memory buffers based on expected inputs but fails to rigorously validate that the actual data present in the buffer meets or exceeds the length indicated by the MsgBytes field before initiating character encoding conversions. Consequently, when the UTF-8 conversion routine executes, it reads beyond the boundaries of the allocated heap memory region. This out-of-bounds read does not typically allow for arbitrary code execution due to its nature as a read-only violation rather than a write operation; however, accessing unmapped or protected memory pages triggers an immediate segmentation fault or access violation exception within the client process.
The operational impact of this vulnerability is primarily focused on availability and service disruption. A malicious actor who controls the RD Gateway can exploit this flaw to cause denial-of-service conditions against connected FreeRDP clients. By sending crafted messages with mismatched length fields, the attacker forces the client application into an unrecoverable error state, resulting in a crash that terminates the remote session abruptly. This disrupts business continuity for users relying on stable remote desktop connections and can be leveraged to target specific infrastructure components if multiple clients are connected simultaneously through the compromised gateway. The severity is heightened by the fact that RD Gateways often act as trusted intermediaries, making it easier for an attacker with control over such a node to inject these malformed packets without triggering immediate suspicion from network security monitoring tools focused on external threats.
In terms of industry classification standards, this vulnerability aligns closely with CWE-125, which defines out-of-bounds read vulnerabilities where software reads data past the end or before the beginning of the intended buffer. It also relates to CWE-20 regarding improper input validation, as the application fails to correctly validate that the declared length matches the actual available data size prior processing. From a tactical perspective within the MITRE ATT&CK framework, this behavior is consistent with techniques used in Denial-of-Service attacks where resource exhaustion or process termination is achieved through malformed inputs rather than brute force methods. The specific context of manipulating protocol fields to trigger crashes falls under adversarial tactics aimed at disrupting communication channels and degrading trust in remote access infrastructure.
Mitigation strategies for this vulnerability require immediate action by system administrators and security teams managing FreeRDP deployments. The primary remediation is to upgrade the FreeRDP client software to version 3.32.0 or later, where developers have implemented stricter validation checks to ensure that buffer lengths are verified against actual data availability before any conversion operations occur. In environments where immediate patching is not feasible due to operational constraints, network-level controls should be employed to restrict access to RD Gateways from untrusted sources. Implementing deep packet inspection solutions capable of detecting anomalous RDP message structures can provide an additional layer of defense by blocking packets with inconsistent length fields before they reach the vulnerable client applications. Furthermore, organizations should review their gateway configurations to ensure that only authorized and trusted gateways are permitted to handle sensitive remote desktop sessions, thereby reducing the attack surface available for this specific exploitation path.