CVE-2023-39355 in FreeRDP
Summary
by MITRE • 08/31/2023
FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Versions of FreeRDP on the 3.x release branch before beta3 are subject to a Use-After-Free in processing `RDPGFX_CMDID_RESETGRAPHICS` packets. If `context->maxPlaneSize` is 0, `context->planesBuffer` will be freed. However, without updating `context->planesBuffer`, this leads to a Use-After-Free exploit vector. In most environments this should only result in a crash. This issue has been addressed in version 3.0.0-beta3 and users of the beta 3.x releases are advised to upgrade. There are no known workarounds for this vulnerability.
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Analysis
by VulDB Data Team • 02/16/2025
The vulnerability CVE-2023-39355 represents a critical use-after-free flaw in FreeRDP versions prior to 3.0.0-beta3, specifically affecting the RDPGFX component responsible for graphics handling in remote desktop connections. This issue occurs during processing of RDPGFX_CMDID_RESETGRAPHICS packets, which are part of the Remote Desktop Protocol's graphics subsystem designed to manage graphics updates and synchronization between client and server. The flaw exists within the memory management logic where the system attempts to free memory resources without properly nullifying the pointer references, creating a scenario where freed memory can be accessed by subsequent operations.
The technical implementation of this vulnerability stems from improper handling of the context->maxPlaneSize variable during graphics reset operations. When this variable equals zero, the code executes a memory deallocation for context->planesBuffer but fails to set the pointer to NULL, leaving a dangling reference. This creates a classic use-after-free condition where subsequent code paths may attempt to access or modify memory that has already been freed, potentially leading to memory corruption. The vulnerability is particularly dangerous because it can be triggered through normal RDP communication patterns, making it exploitable in real-world scenarios where remote desktop connections are established.
The operational impact of this vulnerability extends beyond simple crash conditions, as the use-after-free condition can potentially be leveraged for more sophisticated attacks. While the immediate effect is typically a denial of service through application crashes, the underlying memory corruption opens possibilities for arbitrary code execution or privilege escalation depending on the execution environment. The vulnerability affects all 3.x release branch versions prior to beta3, representing a significant security regression in what should be a stable remote desktop implementation. Attackers could exploit this by establishing a legitimate RDP connection and sending specially crafted graphics reset packets that trigger the memory management flaw.
Mitigation strategies for CVE-2023-39355 require immediate upgrading to FreeRDP version 3.0.0-beta3 or later, as no effective workarounds exist for this particular vulnerability. Organizations using affected FreeRDP versions should implement network segmentation and access controls to limit exposure, while monitoring for suspicious RDP traffic patterns that might indicate exploitation attempts. The fix implemented in version 3.0.0-beta3 addresses the root cause by ensuring proper nullification of the freed pointer, preventing the use-after-free condition. This vulnerability aligns with CWE-416, which specifically addresses use-after-free errors, and represents a common pattern in memory safety issues within network protocol implementations. Security teams should also consider implementing intrusion detection systems that can identify malformed RDPGFX packets targeting this specific vulnerability.