CVE-2026-109951 in FreeRDP
Summary
by MITRE • 10/13/2026
FreeRDP 3.17.1 before 3.32.0 contains a heap buffer over-read vulnerability in DynvcTrackerHandleCreateBack of the freerdp-proxy DRDYNVC channel handler that allows malicious backend RDP servers to read heap memory out of bounds. Attackers can send a CREATE_REQUEST_PDU whose channel name lacks a NUL byte, causing an unbounded snprintf read that leaks memory into proxy logs or crashes the process.
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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 security flaw within the Dynamic Virtual Channel (DYNVVC) subsystem, specifically located in the DynvcTrackerHandleCreateBack function of the freerdp-proxy component. This proxy service acts as an intermediary between clients and backend Remote Desktop Protocol servers, managing various virtual channels to facilitate data exchange. The core technical deficiency lies in how the handler processes channel creation requests received from the remote server side. When a malicious backend RDP server initiates a connection or attempts to establish a new dynamic channel, it sends a CREATE_REQUEST_PDU structure that includes metadata about the channel, including its name. In this specific implementation flaw, the code responsible for handling these incoming requests fails to adequately validate the length and termination of the channel name string provided by the attacker-controlled server.
The technical mechanism of exploitation involves sending a crafted CREATE_REQUEST_PDU where the channel name field is deliberately constructed without a terminating NUL byte. Because the receiving function expects a standard null-terminated C-string, it proceeds to read memory sequentially until it encounters a zero value in adjacent heap memory. This results in an unbounded snprintf operation that reads data beyond the allocated buffer boundaries for the channel name. Consequently, this leads to a heap buffer over-read condition. The immediate operational impact of this flaw is twofold: first, sensitive information from the process heap can be leaked into proxy logs or network responses if the read memory contains identifiable data structures; second, and more critically, reading out-of-bounds memory often corrupts subsequent operations or triggers segmentation faults, leading to a denial of service by crashing the freerdp-proxy process. This undermines the availability of remote desktop services that rely on this proxy infrastructure for secure tunneling or translation between different RDP implementations.
From a classification perspective, this vulnerability aligns with CWE-125, which describes Out-of-bounds Read vulnerabilities where software reads data past the end, or before the beginning, of the intended buffer. The attack vector is categorized under ATT&CK technique T1046, Network Service Discovery, as it involves interacting with a network service to extract information, although in this case, the primary goal may be destabilization via denial of service rather than pure data exfiltration. However, memory disclosure remains a significant risk factor that could potentially aid further exploitation by revealing internal state or cryptographic keys stored on the heap. The vulnerability is particularly dangerous because it allows an attacker who controls the backend RDP server to compromise the integrity and availability of the proxy layer, which might be positioned in front of critical infrastructure or sensitive user endpoints.
Mitigation strategies must prioritize immediate patching to version 3.32.0 or later, where this input validation logic has been corrected to enforce strict bounds checking on all incoming channel names regardless of their source. In environments where upgrading is not immediately feasible, network-level controls such as deep packet inspection firewalls can be configured to detect and block malformed RDP packets that exhibit signs of truncated strings in dynamic channel headers. Additionally, deploying the proxy with restricted logging levels for verbose debug output can mitigate the impact of information leakage by preventing sensitive heap contents from being written to log files during crash scenarios or error handling routines. Regular security audits of third-party dependencies used in remote access infrastructure are essential to ensure that such low-level memory management errors do not persist in production environments, thereby maintaining a robust defense-in-depth posture against protocol-based attacks targeting virtual channel implementations.