CVE-2020-11038 in FreeRDP
Summary
by MITRE
In FreeRDP less than or equal to 2.0.0, an Integer Overflow to Buffer Overflow exists. When using /video redirection, a manipulated server can instruct the client to allocate a buffer with a smaller size than requested due to an integer overflow in size calculation. With later messages, the server can manipulate the client to write data out of bound to the previously allocated buffer. This has been patched in 2.1.0.
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Analysis
by VulDB Data Team • 05/19/2025
The vulnerability CVE-2020-11038 represents a critical security flaw in FreeRDP versions up to and including 2.0.0 that demonstrates a classic integer overflow leading to buffer overflow conditions. This issue specifically manifests within the video redirection functionality of the Remote Desktop Protocol client implementation, creating a pathway for remote code execution through carefully crafted malicious server responses. The vulnerability exists in the client-side buffer allocation logic where integer overflow occurs during size calculations, resulting in insufficient memory allocation that subsequent data writes can overwrite beyond intended boundaries.
The technical exploitation of this vulnerability begins with a manipulated server that sends specially crafted video redirection messages to a vulnerable FreeRDP client. During the video redirection process, the client calculates buffer sizes based on data provided by the server, but an integer overflow in this calculation causes the client to allocate a buffer that is significantly smaller than the amount of data the server intends to transmit. This mathematical overflow occurs when the size calculation exceeds the maximum value that can be represented by the integer type used in the allocation routine, typically resulting in a wraparound to a much smaller value. The subsequent data transmission from the malicious server can then overwrite memory locations adjacent to the improperly sized buffer, potentially leading to arbitrary code execution or system instability.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to encompass potential remote code execution capabilities that could allow attackers to compromise systems running vulnerable FreeRDP clients. Attackers can leverage this flaw to execute malicious code within the context of the affected client process, potentially gaining unauthorized access to systems, escalating privileges, or establishing persistent backdoors. The vulnerability affects any system that utilizes FreeRDP for remote desktop connections with video redirection enabled, making it particularly concerning for enterprise environments where remote access solutions are prevalent. Organizations using older versions of FreeRDP for remote desktop connectivity face significant risk exposure, especially when connecting to untrusted or potentially compromised servers.
This vulnerability maps directly to CWE-190, Integer Overflow or Wraparound, and CWE-121, Stack-based Buffer Overflow, within the Common Weakness Enumeration framework, demonstrating how integer arithmetic errors can cascade into more severe memory corruption vulnerabilities. The attack pattern aligns with ATT&CK technique T1210, Exploitation of Remote Services, and T1059, Command and Scripting Interpreter, as attackers can leverage the buffer overflow to execute arbitrary commands. Organizations should prioritize immediate patching to version 2.1.0 or later, which implements proper integer overflow checks and bounds validation in buffer allocation routines. Additional mitigations include network segmentation to limit exposure, disabling video redirection when connecting to untrusted servers, and implementing network monitoring to detect suspicious traffic patterns associated with exploitation attempts. The vulnerability underscores the importance of proper input validation and integer overflow protection in security-critical applications, particularly those handling untrusted network data in multimedia streaming scenarios.