CVE-2023-40576 in FreeRDP
Summary
by MITRE • 09/01/2023
FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Affected versions are subject to an Out-Of-Bounds Read in the `RleDecompress` function. This Out-Of-Bounds Read occurs because FreeRDP processes the `pbSrcBuffer` variable without checking if it contains data of sufficient length. Insufficient data in the `pbSrcBuffer` variable may cause errors or crashes. This issue has been addressed in version 3.0.0-beta3. Users are advised to upgrade. There are no known workarounds for this issue.
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Analysis
by VulDB Data Team • 03/13/2026
The CVE-2023-40576 vulnerability affects FreeRDP, a widely-used open-source implementation of Microsoft's Remote Desktop Protocol that enables remote desktop connections across various platforms. This vulnerability manifests as an out-of-bounds read condition within the RleDecompress function, which is responsible for decompressing RLE (Run-Length Encoding) data during RDP session processing. The flaw represents a critical security weakness that can potentially lead to system instability, crashes, or even remote code execution depending on the exploitation context. The vulnerability specifically targets the pbSrcBuffer variable processing where the software fails to validate buffer boundaries before attempting to read data from it.
The technical root cause of this vulnerability stems from inadequate input validation within the RleDecompress function where FreeRDP processes compressed data streams without proper boundary checking mechanisms. When the pbSrcBuffer contains insufficient data to satisfy the decompression requirements, the function attempts to read beyond the allocated buffer limits, resulting in unpredictable behavior. This type of vulnerability falls under CWE-129, which specifically addresses insufficient validation of length of buffers, and can be categorized as a memory safety issue that aligns with ATT&CK technique T1059.007 for command and scripting interpreter. The vulnerability is particularly concerning because RDP is a fundamental protocol for remote administration and access, making this flaw exploitable in various attack scenarios including denial of service and potentially more sophisticated exploitation techniques.
The operational impact of CVE-2023-40576 extends beyond simple system crashes, as it represents a potential entry point for attackers seeking to compromise remote desktop environments. Organizations using FreeRDP for remote access, system administration, or virtual desktop infrastructure deployments face significant risk exposure, particularly in environments where RDP is extensively used. The vulnerability can be triggered through malformed RDP data streams, making it potentially exploitable in man-in-the-middle scenarios or when processing untrusted RDP connection data. Attackers could leverage this flaw to cause service disruption, create denial of service conditions, or potentially establish footholds within network environments where RDP access is permitted. The lack of known workarounds forces organizations to rely entirely on the vendor-provided patch, making this vulnerability particularly dangerous for systems that cannot be immediately updated.
The remediation strategy for this vulnerability centers exclusively on upgrading to FreeRDP version 3.0.0-beta3 or later, as this release contains the necessary patches to address the buffer boundary checking issues in the RleDecompress function. Organizations should prioritize this upgrade as a critical security measure, particularly for systems handling RDP connections or remote desktop access. Security teams should implement monitoring for any unusual RDP connection behavior or service disruptions that might indicate exploitation attempts. Additionally, network segmentation and access controls should be reviewed to limit exposure of systems running FreeRDP, while implementing proper input validation and boundary checking in any custom RDP-related implementations. The vulnerability highlights the importance of robust memory safety practices in network protocol implementations and underscores the need for thorough input validation in all data processing functions. Organizations should also consider implementing intrusion detection systems that can identify potential exploitation attempts targeting RDP services, as the out-of-bounds read could potentially be leveraged in more advanced attack vectors.