CVE-2026-109943 in FreeRDP
Summary
by MITRE • 10/13/2026
FreeRDP 3.29.0 before 3.32.0 contains a double free in the client's async-update message proxy, which shallow-copies the parser-owned PolygonSC or PolygonCB points array when numPoints is zero, so both the queue consumer and parser cleanup free it. A malicious RDP server can send a point-bearing polygon order followed by a zero-point order to crash a client with +async-update enabled.
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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 memory management flaw located within the asynchronous update message proxy mechanism of the Remote Desktop Protocol client implementation. This specific defect is classified under CWE-415, which denotes Double Free errors, and aligns with MITRE ATT&CK technique T1499, specifically Endpoint Denial of Service via resource exhaustion or crash mechanisms. The root cause stems from an improper handling of polygon drawing commands when the number of points specified in a PolygonCB or PolygonSC structure is zero. In these specific instances, the code performs a shallow copy of the parser-owned array containing point coordinates rather than creating a deep copy with independent memory allocation. This architectural decision assumes that the underlying data will remain valid for the duration of its usage by both the parsing engine and the asynchronous processing queue, but fails to account for lifecycle mismatches between these two components.
During normal operation, when an RDP server sends drawing commands, they are processed through a parser that allocates memory structures to hold geometric data such as polygon points. These structures are then passed to an internal message proxy responsible for handling asynchronous updates, which allows the client to process display updates without blocking the main UI thread. The vulnerability is triggered specifically when a malicious RDP server sends two consecutive orders: first, a polygon order that includes point data and allocates memory for it, followed immediately by another polygon order where the numPoints field is set to zero. In this scenario, the proxy logic incorrectly applies the shallow copy mechanism even when no points are present or when reusing buffers in a way that leaves pointers dangling. Consequently, both the queue consumer thread responsible for rendering and the parser cleanup routine attempt to deallocate the same memory block independently.
The operational impact of this double free condition is severe, leading directly to application instability and potential remote code execution depending on heap state exploitation conditions. In most typical scenarios involving FreeRDP clients with the +async-update flag enabled, the immediate result is a segmentation fault or access violation that crashes the client application. This constitutes a denial-of-service attack vector where an attacker can disrupt user productivity by simply sending crafted RDP packets containing malformed polygon orders. While the primary observed effect is a crash, double free vulnerabilities are historically significant because they allow attackers to manipulate heap metadata during the second deallocation phase. By carefully controlling memory allocation patterns before and after triggering the vulnerability, an adversary may achieve arbitrary write primitives or code execution, although exploitation complexity varies based on operating system protections such as ASLR and DEP/NX bits.
Mitigation strategies for this vulnerability primarily involve upgrading FreeRDP to version 3.32.0 or later, where the memory management logic has been corrected to ensure proper ownership semantics and independent allocation of data structures within the async-update proxy. For environments unable to patch immediately, disabling asynchronous updates by omitting the +async-update flag during client connection can serve as a temporary workaround, although this may degrade performance for high-latency connections or complex graphical workloads. Security teams should also monitor network traffic for anomalous RDP packet sequences that involve rapid succession of polygon drawing commands with zero-point specifications, which could indicate active exploitation attempts against unpatched systems. Regular vulnerability scanning and patch management processes are essential to maintain the integrity of remote desktop infrastructure against such memory corruption flaws.