CVE-2026-111881 in FreeRDP
Summary
by MITRE • 10/17/2026
FreeRDP from 3.14.1 before 3.32.0 contains an integer underflow in the WinPR BMP writer, where a mismatched stride calculation passes SIZE_MAX - 3 to Stream_Zero for sub-byte images. A malicious RDP clipboard peer can return a crafted 1-bpp BMP processed by clipboard_synthesize_image_format_to_bmp for CF_DIB/CF_DIBV5, crashing the client or causing an out-of-bounds write.
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Analysis
by VulDB Data Team • 10/17/2026
The vulnerability identified in FreeRDP versions prior to 3.32.0 represents a critical security flaw within the WinPR BMP writer component, specifically affecting how bitmap data is processed during clipboard operations over Remote Desktop Protocol connections. This issue stems from an integer underflow condition that occurs when calculating the stride for image buffers. The stride calculation fails to properly account for sub-byte images, particularly those with one bit per pixel formats such as CF_DIB or CF_DIBV5. When a malicious RDP clipboard peer submits crafted bitmap data, the system incorrectly computes the buffer size required for processing, resulting in the passage of SIZE_MAX minus three bytes to the Stream_Zero function. This erroneous calculation leads to significant memory management failures that compromise the integrity and stability of the client application.
From a technical perspective, the core issue lies in the mishandling of small image dimensions where pixel data does not align with standard byte boundaries. The WinPR library is responsible for converting various clipboard formats into BMP structures for display or further processing within the FreeRDP environment. During this conversion process via the clipboard_synthesize_image_format_to_bmp function, the stride calculation logic assumes a certain alignment that does not hold true for 1-bpp images. Consequently, instead of allocating sufficient memory to safely write the bitmap data, the system allocates an excessively large buffer or misinterprets existing buffers due to the underflowed size value. This discrepancy allows for out-of-bounds writes when the BMP writer attempts to populate the buffer with pixel data derived from the malicious input. The resulting memory corruption can lead to application crashes, denial of service conditions, and potentially arbitrary code execution if an attacker can carefully control the overwritten memory regions.
The operational impact of this vulnerability is severe, primarily affecting users who interact with untrusted or compromised remote desktop environments. Since clipboard sharing is a common feature in RDP sessions for productivity purposes, attackers can exploit this flaw by simply pasting maliciously crafted bitmap content into their side of the session. The victim's FreeRDP client will then attempt to process this data through the vulnerable BMP writer routine. Successful exploitation results in immediate instability or termination of the remote desktop application, disrupting business continuity and potentially causing loss of unsaved work. In more sophisticated attack scenarios involving memory corruption techniques, an attacker might leverage the out-of-bounds write to execute arbitrary code on the client machine, thereby gaining unauthorized access to sensitive information or using the compromised system as a pivot point for further network intrusion.
This vulnerability aligns with CWE-190, which describes integer overflow or wraparound resulting in incorrect behavior due to arithmetic operations exceeding the maximum representable value of an integer type. Although technically classified here as an underflow leading to excessive allocation or misinterpretation, it falls under the broader category of improper handling of numeric values that leads to memory safety violations. Furthermore, from a threat modeling perspective consistent with MITRE ATT&CK frameworks, this flaw facilitates initial access and execution capabilities through technique T1059 Command and Scripting Interpreter if code execution is achieved via buffer overflow exploitation methods commonly associated with such memory corruption bugs. It also relates to CWE-787 Out-of-bounds Write, as the primary consequence of the flawed stride calculation is writing data beyond the intended boundaries of allocated memory structures.
Mitigation strategies for this vulnerability focus primarily on software updates and configuration hardening. Organizations utilizing FreeRDP must immediately upgrade to version 3.32.0 or later where these integer arithmetic issues in the BMP writer have been corrected by developers who implemented stricter bounds checking and proper stride calculations for all pixel depth formats, including sub-byte images like 1-bpp. For environments unable to patch immediately due to dependency constraints, network-level controls should be employed to restrict clipboard sharing capabilities between untrusted endpoints and internal systems. Disabling the CF_DIB and CF_DIBV5 clipboard format transfers via Group Policy or configuration files can prevent the specific code path from being triggered by malicious peers. Additionally, deploying intrusion detection signatures that monitor for anomalous RDP traffic patterns associated with oversized or malformed bitmap payloads may provide an additional layer of defense against exploitation attempts while patching efforts are underway.