CVE-2026-69159 in FreeRDP
Summary
by MITRE • 08/19/2026
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to 3.29.0, planar_decompress_plane_rle and planar_decompress_plane_rle_only in libfreerdp/codec/planar.c verify that a control byte exists but do not verify that the source buffer contains the zero to fifteen raw bytes declared by that control byte. A malicious RDP server can send a truncated planar bitmap or surface update whose final control byte claims additional raw bytes, causing the decoder to read beyond pSrcData while processing a color plane. This can crash the client and may disclose adjacent memory. This issue is fixed in version 3.29.0.
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability identified in FreeRDP prior to version 3.29.0 represents a critical boundary condition error within the planar bitmap decoding logic, specifically affecting the functions planar_decompress_plane_rle and planar_decompress_plane_rle_only located in libfreerdp/codec/planar.c. This flaw stems from an incomplete validation of input data during the decompression process for Remote Desktop Protocol (RDP) connections. While the implementation correctly verifies the existence of a control byte that dictates how subsequent raw bytes should be interpreted, it fails to perform a bounds check on the source buffer relative to the number of raw bytes declared by that control byte. This oversight creates a scenario where the decoder assumes the presence of data that may not actually exist in the provided memory buffer, leading to an out-of-bounds read operation when processing color planes during RDP session updates.
From a technical perspective, this issue is classified as CWE-125: Out-of-bounds Read, which occurs when software reads from a location outside the bounds of allocated memory. The specific mechanism involves the handling of truncated planar bitmaps or surface update packets sent by an attacker-controlled malicious RDP server. When such a packet contains a final control byte that claims additional raw bytes beyond the actual end of the source buffer pSrcData, the decoder proceeds to read from adjacent memory locations without verifying if those locations are valid or accessible. This behavior violates fundamental principles of secure coding regarding input validation and boundary checking, allowing an external actor to influence the program's execution flow by supplying malformed data that triggers unauthorized memory access patterns.
The operational impact of this vulnerability is severe, primarily manifesting as a denial of service through client application crashes due to segmentation faults or illegal memory access violations. However, beyond simple instability, the out-of-bounds read poses significant confidentiality risks. By reading adjacent memory contents, an attacker may potentially disclose sensitive information stored in those locations, such as cryptographic keys, session tokens, or other private data belonging to the user or system running FreeRDP. This aligns with ATT&CK technique T1083: File and Directory Discovery, where adversaries seek to gather environmental information through memory scraping techniques facilitated by buffer over-read vulnerabilities. The ability to leak adjacent memory contents transforms a simple crash bug into a potential vector for data exfiltration or further exploitation depending on the specific context of the running application's memory layout.
Mitigation strategies center primarily on upgrading FreeRDP to version 3.29.0 or later, where this boundary check has been implemented and corrected by the development team. For environments unable to immediately upgrade, network-level filtering can provide a temporary layer of defense by inspecting RDP traffic for anomalies in planar bitmap structures, although deep packet inspection capabilities are required to effectively parse these complex protocol elements. Developers integrating FreeRDP into custom applications should also ensure that their build configurations utilize the latest stable release and consider implementing additional runtime memory protection mechanisms such as Address Sanitizer during testing phases to detect similar boundary violations early in the development lifecycle before deployment.