CVE-2026-67301 in FreeRDP
Summary
by MITRE • 08/01/2026
FreeRDP before 3.29.0 contains out-of-bounds read vulnerabilities in the async update message proxy for the PolygonSC and PolygonCB primary drawing orders. When AsyncUpdate is enabled (e.g., xfreerdp /async-update), update_message_PolygonSC() and update_message_PolygonCB() allocate a fresh points array but copy point data from the address of the order structure instead of from polygonSC->points / polygonCB->points, resulting in a client-side out-of-bounds read. A malicious or compromised RDP server sending crafted PolygonSC/PolygonCB update orders can trigger memory disclosure or a client crash.
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Analysis
by VulDB Data Team • 08/01/2026
The vulnerability under discussion represents a critical out-of-bounds read flaw in FreeRDP versions prior to 3.29.0, specifically affecting the asynchronous update message proxy functionality within the PolygonSC and PolygonCB primary drawing orders. This issue manifests when the AsyncUpdate feature is enabled through configurations such as xfreerdp /async-update, creating a dangerous condition where client-side memory access violations can occur during remote desktop protocol operations. The flaw resides in the implementation of update_message_PolygonSC() and update_message_PolygonCB() functions, which demonstrate improper memory handling when processing polygon drawing orders.
The technical root cause stems from incorrect pointer arithmetic within the drawing order processing logic where these functions allocate fresh points arrays but subsequently copy data from the address of the order structure rather than from the intended polygonSC->points or polygonCB->points fields. This fundamental error in memory management creates a scenario where the client attempts to read beyond the bounds of allocated memory regions, potentially exposing sensitive data through memory disclosure or causing application crashes that disrupt legitimate remote desktop sessions.
From an operational perspective, this vulnerability presents significant security implications within enterprise environments that rely on FreeRDP for remote access solutions. The attack vector requires a malicious or compromised RDP server to craft specially designed PolygonSC/PolygonCB update orders, making it particularly dangerous in scenarios where network traffic is not properly secured or where trusted RDP servers might be compromised through other means. The potential impact extends beyond simple service disruption to include information disclosure that could reveal sensitive memory contents, including credentials, session data, or other confidential information stored in the client's memory space.
This vulnerability aligns with CWE-125 Out-of-Bounds Read and represents a classic example of improper input validation in graphical rendering components. The issue demonstrates how seemingly benign drawing order processing can become a vector for more serious security consequences when proper bounds checking is omitted. From an attacker's perspective, this flaw maps to techniques described in the MITRE ATT&CK framework under T1059 Command and Scripting Interpreter and potentially T1046 Network Service Scanning, as it enables adversaries to manipulate remote desktop protocol communications in ways that can expose system internals.
Mitigation strategies should focus on immediate patching of FreeRDP installations to version 3.29.0 or later where the out-of-bounds read has been corrected through proper pointer handling and bounds validation. Organizations should also consider implementing network segmentation and access controls to limit exposure to potentially compromised RDP servers, while monitoring for unusual RDP traffic patterns that might indicate exploitation attempts. Additionally, disabling AsyncUpdate functionality when not strictly required provides a temporary workaround until full patches are deployed across all affected systems. The vulnerability highlights the importance of thorough memory management practices in graphical protocol implementations and underscores the need for comprehensive security testing of rendering components within remote desktop solutions.