CVE-2026-109256 in FreeRDP
Summary
by MITRE • 10/12/2026
FreeRDP 3.10.0 through 3.32.2 contains a heap buffer overflow in the WinPR png_write_data callback that writes past the buffer after a realloc failure. A malicious RDP clipboard peer can supply a large CF_DIB image that triggers out-of-bounds memcpy during PNG conversion, causing a client crash.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified within FreeRDP versions 3.10.0 through 3.32.2 represents a critical heap buffer overflow located in the WinPR png_write_data callback function. This flaw arises from improper memory management during the processing of PNG image data, specifically when the system attempts to reallocate buffers for writing pixel data. The root cause lies in the failure to adequately validate or handle scenarios where a realloc operation fails to expand the allocated memory block as expected. In such cases, the application continues to execute write operations based on an incorrect assumption about buffer boundaries, leading directly to out-of-bounds writes that corrupt adjacent heap memory structures.
From a technical perspective, this issue is classified under CWE-122, which denotes a heap-based buffer overflow. The vulnerability is triggered when a malicious Remote Desktop Protocol (RDP) clipboard peer supplies a specially crafted large CF_DIB image format payload. Upon receipt, the FreeRDP client attempts to convert this image data into PNG format for display or further processing. During this conversion process, the png_write_data callback is invoked to handle the output stream. If the underlying memory allocation mechanism encounters an error during reallocation, such as insufficient contiguous free space or a system limit being reached, the pointer returned may not reflect the new intended size correctly, yet subsequent memcpy operations proceed using the original or miscalculated length parameters. This results in writing data beyond the allocated heap region, potentially overwriting critical metadata like allocation headers or adjacent object pointers.
The operational impact of this vulnerability is primarily a denial of service condition manifested as a client crash. Because the overflow occurs within the clipboard handling subsystem, which processes untrusted input from remote peers during standard RDP sessions, an attacker can exploit this flaw remotely without requiring authentication in many configurations. By sending the malicious CF_DIB image through the clipboard synchronization feature, the attacker forces the target application to execute the flawed code path. The resulting memory corruption typically leads to immediate segmentation faults or access violations within the FreeRDP client process, causing it to terminate unexpectedly. While heap overflows can sometimes lead to arbitrary code execution if specific exploitation techniques are applied, in this context, the primary observed effect is service disruption due to application instability and crash.
This vulnerability aligns with MITRE ATT&CK technique T1059.007, which covers command and script interpretation via scripting languages or embedded objects, although here it manifests as a resource exhaustion vector rather than direct code execution. It also relates to CWE-400, concerning uncontrolled resource consumption, as the trigger involves large data inputs that stress memory allocation mechanisms. The flaw highlights significant gaps in defensive programming practices regarding error handling during dynamic memory management operations within multimedia processing libraries integrated into remote desktop clients.
To mitigate this risk, organizations deploying FreeRDP must ensure they are running patched versions beyond 3.32.2 where the realloc failure paths have been corrected to properly check return values and adjust buffer sizes or abort safely before performing writes. Administrators should also consider implementing network-level access controls to restrict RDP connections to trusted sources only, thereby reducing the attack surface for clipboard-based exploits. Additionally, enabling strict input validation on clipboard data at the gateway level can prevent malformed images from reaching vulnerable client instances. Regular patch management and monitoring of application logs for unexpected crashes are essential operational security measures while transitioning to secure versions.