CVE-2026-109680 in FreeRDP
Summary
by MITRE • 10/13/2026
FreeRDP 3.18.0 before 3.32.0 has a heap-based out-of-bounds write in freerdp_interruptible_get_line, which shrinks the buffer to 32 bytes while keeping a pre-filled suggested username's length as its write offset. A malicious or compromised ARM routing service can return a long redirectedUsername that reaches the CLI credential prompt, crashing the client when the user types input.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability identified in FreeRDP versions prior to 3.32.0 represents a critical heap-based out-of-bounds write flaw located within the freerdp_interruptible_get_line function. This specific memory corruption issue arises from an improper handling of buffer boundaries during the processing of user input, particularly when interacting with credential prompts. The core technical defect involves a logic error where the internal buffer is forcibly shrunk to a fixed size of thirty-two bytes. However, the write offset for this operation is not recalculated or validated against this new limit but instead retains the length value derived from a pre-filled suggested username provided by the remote server. This discrepancy creates a scenario where the application attempts to write data at an index that exceeds the allocated memory space, leading directly to heap corruption and potential arbitrary code execution if exploited effectively.
The operational impact of this vulnerability is significant for users connecting through environments involving ARM routing services or similar infrastructure components capable of manipulating connection parameters. A malicious actor controlling such a service can craft a response containing an excessively long redirectedUsername field. When the FreeRDP client processes this input, it triggers the flawed logic in freerdp_interruptible_get_line. The mismatch between the truncated buffer size and the oversized write offset causes the application to crash upon user interaction with the CLI credential prompt. While immediate exploitation for remote code execution requires further conditions such as specific heap layout configurations or additional vulnerabilities, the guaranteed denial of service via client crash poses a severe availability risk. This disruption can halt productivity and potentially expose users to secondary attacks if they are forced to restart their sessions in an unsecured environment.
From a classification perspective, this vulnerability aligns with CWE-120, which denotes buffer copy without checking size limits, specifically manifesting as a heap-based out-of-bounds write. The attack vector leverages the trust placed in remote server responses during the authentication phase of the Remote Desktop Protocol connection process. In terms of adversary tactics and techniques, this flaw can be mapped to ATT&CK technique T1059, Command and Scripting Interpreter, if used as part of a broader exploitation chain involving arbitrary code execution. More immediately, it relates to availability-focused attacks under the impact category, disrupting legitimate access to remote resources by crashing the client application before authentication is completed.
Mitigation strategies primarily involve upgrading FreeRDP to version 3.32.0 or later, where this logic error has been corrected through proper validation of buffer sizes against write offsets. Organizations relying on FreeRDP should ensure their deployment pipelines enforce strict version controls and automated patching mechanisms to prevent exposure to known memory corruption flaws. Additionally, network security teams should consider implementing deep packet inspection rules that flag anomalous lengths in RDP negotiation packets, particularly those involving redirected username fields exceeding standard limits. This defensive measure can help detect attempts to exploit this vulnerability before the client processes the malicious payload. Regular auditing of third-party dependencies and maintaining an inventory of all FreeRDP instances across the enterprise infrastructure is essential for comprehensive risk management against such memory safety issues.