CVE-2026-121964 in FreeRDP
Summary
by MITRE • 11/04/2026
FreeRDP before 3.32.2 contains a heap-based buffer overflow in the RD Gateway RPC client, where rpc_client_recv_fragment writes BIND_ACK and ALTER_CONTEXT_RESP fragments into a persistent PDU stream after checking only total capacity rather than remaining capacity from the current stream position. A malicious or compromised RD Gateway can send crafted RPC fragments with manipulated alloc_hint and frag_length values to overwrite client heap memory with attacker-controlled data, causing a crash or potentially arbitrary code execution.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in FreeRDP versions prior to 3.32.2 represents a critical security flaw within the Remote Desktop Protocol Gateway RPC client implementation. This issue is classified as a heap-based buffer overflow, specifically located in the rpc_client_recv_fragment function responsible for processing incoming Remote Procedure Call fragments. The core technical deficiency stems from an incorrect boundary check during memory allocation and data copying operations. When receiving BIND_ACK or ALTER_CONTEXT_RESP protocol fragments, the software validates that the total capacity of the destination buffer is sufficient to hold the new data but fails to account for the current position within a persistent Protocol Data Unit stream. This oversight means that if multiple fragments are processed sequentially without resetting the offset correctly, the cumulative write operation can exceed the allocated heap memory boundaries.
An attacker who controls or compromises an RD Gateway server can exploit this logic error by crafting malicious RPC fragments with manipulated alloc_hint and frag_length values. By carefully calculating these parameters, the adversary can force the client to write data beyond the bounds of the intended buffer into adjacent heap regions. This out-of-bounds write allows for arbitrary memory corruption, which typically results in a denial of service through application crash due to segmentation faults or corrupted heap metadata. However, with precise exploitation techniques involving heap grooming and specific payload construction, this vulnerability can potentially be leveraged to achieve remote code execution on the client system by overwriting function pointers or exception handling structures within the process memory space.
From an industry standard perspective, this flaw aligns closely with CWE-120 Buffer Copy without Checking Size of Input Classic buffer overflow and CWE-787 Out-of-bounds Write. The attack vector involves interacting with a network service that processes untrusted input from a potentially compromised server, which maps to the MITRE ATT&CK technique T1557 Adversary-in-the-Middle where an attacker intercepts or manipulates communications between two parties. Furthermore, the exploitation of heap memory corruption for code execution relates to techniques such as Heap Spraying and Overwriting Function Pointers found in advanced persistent threat campaigns targeting remote desktop infrastructure.
The operational impact is severe given that FreeRDP is a widely used open-source implementation of Microsoft's Remote Desktop Protocol. Users connecting through an RD Gateway are exposed to this risk if the gateway itself has been compromised or if they connect to a maliciously configured server acting as a man-in-the-middle. The ability to execute arbitrary code on the client machine provides attackers with full control over the user environment, enabling data exfiltration, lateral movement within internal networks, and persistence mechanisms. This is particularly dangerous in enterprise environments where remote desktop connections are frequently established through gateways that may have varying levels of security hardening or monitoring.
Mitigation strategies primarily involve upgrading to FreeRDP version 3.32.2 or later, which includes the necessary code corrections to validate remaining buffer capacity relative to the current stream position before performing writes. Organizations should also implement network segmentation and strict access controls for RD Gateway servers to limit exposure to untrusted networks. Additionally, deploying endpoint detection and response solutions that monitor for anomalous heap activity or unexpected memory modifications can provide an additional layer of defense against exploitation attempts while patching efforts are underway. Regular security audits of remote desktop configurations and ensuring that all components in the RDP chain are kept up-to-date with vendor releases remain essential practices to maintain a robust security posture against such protocol-level vulnerabilities.