CVE-2026-121950 in FreeRDP
Summary
by MITRE • 11/04/2026
FreeRDP before 3.32.2 does not check the product of surface dimensions in gdi_CreateSurface when handling an RDPGFX CREATE_SURFACE PDU, causing an integer wrap and heap buffer overflow on 32-bit builds and an approximately 4 GiB allocation on 64-bit builds. A malicious RDP server can send a CREATE_SURFACE PDU with width and height 32766 to a connecting client to corrupt heap memory or cause a denial of service.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in FreeRDP versions prior to 3.32.2 represents a critical integer overflow condition located within the gdi_CreateSurface function, which is responsible for handling Remote Desktop Graphics (RDPGFX) CREATE_SURFACE Protocol Data Units. This flaw stems from an insufficient validation of input parameters provided by the remote server during the initialization of graphical surface resources. Specifically, when processing dimensions such as width and height set to 32766, the application calculates the total memory required for the surface buffer without accounting for potential integer wraparound effects on 32-bit architectures or excessive allocation sizes on 64-bit systems. This lack of bounds checking allows an attacker to manipulate internal arithmetic operations, leading to severe memory corruption or resource exhaustion scenarios that compromise the stability and security of the client application.
On 32-bit builds, the multiplication of surface dimensions results in an integer wraparound due to the limited address space and data type constraints inherent to this architecture. The calculated size wraps around to a significantly smaller value than intended by the actual pixel count, causing the system to allocate only a small portion of the required heap memory. However, subsequent operations attempt to write or access data based on the full logical dimensions rather than the truncated allocation size. This discrepancy leads directly to a heap buffer overflow, where writes exceed the bounds of the allocated memory block. Such overflows can corrupt adjacent heap metadata, overwrite function pointers, or alter critical application state variables, potentially enabling arbitrary code execution if an attacker can carefully craft subsequent allocations and exploits to leverage this corruption for control flow hijacking.
In contrast, on 64-bit builds, the integer overflow manifests differently due to the larger address space available. The multiplication of large dimension values results in a massive allocation request, approximately four gigabytes of contiguous heap memory. While this may not immediately cause code execution through buffer overflows, it poses a severe denial-of-service risk by exhausting system resources or triggering out-of-memory conditions within the FreeRDP client process. This resource exhaustion can crash the application, disrupt ongoing remote sessions, and potentially impact other processes sharing the same memory pool if the allocation fails partially or causes fragmentation issues that degrade overall system performance.
From an industry standard perspective, this vulnerability aligns with CWE-190 Integer Overflow or Wraparound, as the root cause is the failure to handle arithmetic operations correctly when inputs approach maximum limits for their data types. Furthermore, it relates closely to CWE-787 Out-of-bounds Write in 32-bit contexts where memory corruption occurs due to size miscalculation. In terms of offensive security frameworks such as MITRE ATT&CK, this flaw facilitates techniques associated with Initial Access and Execution via Remote Services, specifically leveraging the RDP protocol's graphical subsystems to exploit client-side applications. Attackers can utilize this vulnerability during active sessions or potentially in pre-authentication scenarios depending on how early in the handshake process the CREATE_SURFACE PDU is processed, allowing for remote exploitation without user interaction beyond establishing a connection.
Mitigation strategies primarily involve upgrading FreeRDP to version 3.32.2 or later, where developers have implemented rigorous input validation and size checks before performing arithmetic operations related to memory allocation. Administrators should ensure that all client endpoints are patched promptly to prevent exposure to malicious RDP servers configured to exploit this flaw. Additionally, deploying network-level authentication and restricting access to trusted RDP sources can reduce the attack surface by limiting which entities can send crafted PDUs to vulnerable clients. For environments where immediate patching is not feasible, implementing strict firewall rules or intrusion detection signatures that monitor for anomalous CREATE_SURFACE requests with unusually large dimension values may provide a temporary layer of defense against exploitation attempts targeting this specific integer overflow condition.