CVE-2026-109242 in FreeRDP
Summary
by MITRE • 10/12/2026
FreeRDP before 3.0.0 and 3.6.0 before 3.32.0 renders uninitialized heap memory from un-decoded progressive tiles because the tile->current buffer is allocated without zeroing. A malicious RDP server can send a crafted WBT_TILE_FIRST then WBT_TILE_UPGRADE sequence to paint heap bytes onscreen or abort the client process.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified in FreeRDP versions prior to 3.0.0 and between 3.6.0 and 3.32.0 represents a critical memory safety flaw rooted in improper initialization of dynamic memory allocations during the rendering of Remote Desktop Protocol graphics data. Specifically, the defect occurs within the handling of progressive tile decoding for Windows Bitmap Compression (WBT) images. When FreeRDP processes incoming graphical updates from an RDP server, it allocates buffers to store intermediate and final decoded image tiles. In this specific code path, the buffer designated as current is allocated using standard memory allocation functions that do not guarantee zeroed content. Consequently, any bytes remaining in the heap from previous allocations are retained within this newly minted buffer until they are explicitly overwritten by valid decoding data.
The operational impact of this uninitialized memory exposure becomes apparent when a malicious RDP server crafts specific sequences of WBT_TILE_FIRST and WBT_TILE_UPGRADE messages. These messages instruct the client to decode partial or upgraded tile data. Because the underlying buffer was not cleared, any portion of the decoded image that is smaller than the allocated buffer size will leave residual heap contents intact in the unused portions of the memory region. When FreeRDP proceeds to render this tile on screen, it copies these uninitialized bytes directly into the display output without sanitization. This results in a direct information disclosure vulnerability where sensitive data from other processes or previous operations within the same application process can be rendered visibly on the user's monitor.
Beyond simple visual leakage of heap contents, the presence of uninitialized memory introduces significant stability risks for the client application. The unpredictable nature of heap state means that certain byte patterns may trigger logic errors during subsequent processing steps, such as bounds checking or format conversion routines. This unpredictability can lead to process termination via an abort signal if invalid data structures are encountered downstream in the rendering pipeline. Furthermore, depending on how the uninitialized bytes interact with other memory management operations, there is a potential for exploitation leading to arbitrary code execution, although the primary documented impact remains information disclosure and denial of service through application crash.
From a classification perspective, this vulnerability aligns closely with CWE-908, which describes the use of uninitialized memory resources that can lead to unpredictable behavior or security breaches. It also relates to CWE-457 regarding the use of an uninitialized variable within a logic flow. In terms of adversary tactics and techniques, this flaw facilitates reconnaissance activities by allowing an attacker to map out internal application states and potentially extract cryptographic keys or authentication tokens stored in adjacent heap memory regions. This aligns with ATT&CK technique T1005, which covers data from local system retrieval through indirect means such as reading unallocated memory spaces that happen to contain sensitive artifacts.
Mitigation strategies for this vulnerability are primarily focused on software updates and defensive coding practices. The most effective remediation is to upgrade FreeRDP to version 3.0.0 or later, specifically ensuring the installation of a build newer than 3.32.0 where the allocation routines have been patched to zero out memory buffers before use. For environments unable to immediately patch, implementing network-level access controls to restrict RDP connections to trusted servers can mitigate exposure. Additionally, developers should enforce strict initialization policies for all dynamic allocations in graphics processing pipelines, ensuring that every buffer intended for rendering is explicitly cleared using functions like memset prior to any partial data writes. Regular security audits of memory management code paths are essential to prevent similar uninitialized memory exposures in future releases.