CVE-2020-11047 in FreeRDP
Summary
by MITRE
In FreeRDP after 1.1 and before 2.0.0, there is an out-of-bounds read in autodetect_recv_bandwidth_measure_results. A malicious server can extract up to 8 bytes of client memory with a manipulated message by providing a short input and reading the measurement result data. This has been patched in 2.0.0.
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Analysis
by VulDB Data Team • 10/15/2020
The vulnerability CVE-2020-11047 represents a critical out-of-bounds read flaw in FreeRDP versions between 1.1 and 2.0.0, specifically within the autodetect_recv_bandwidth_measure_results function. This issue arises from insufficient input validation when processing bandwidth measurement results from remote servers, creating a pathway for malicious actors to extract sensitive client memory contents. The vulnerability manifests when a compromised server sends a crafted message with insufficient data payload, allowing the client application to read beyond allocated memory boundaries and potentially access up to 8 bytes of adjacent memory locations.
The technical implementation of this flaw demonstrates a classic buffer over-read vulnerability that falls under the Common Weakness Enumeration category CWE-125, which describes out-of-bounds read conditions where programs access memory beyond the boundaries of allocated buffers. The flaw occurs during the automatic bandwidth detection process that FreeRDP employs to optimize remote desktop connections, making it particularly dangerous as it can be triggered during normal connection establishment. Attackers exploit this by crafting specially formatted bandwidth measurement responses that contain fewer bytes than expected, causing the client to read uninitialized or adjacent memory regions during result processing.
From an operational perspective, this vulnerability presents significant security implications for organizations relying on FreeRDP for remote desktop connectivity. The memory extraction capability could potentially expose sensitive information such as cryptographic keys, session tokens, or other confidential data stored in adjacent memory locations. The attack vector is particularly concerning because it requires only a malicious server to be reachable by the client, meaning that even a compromised or untrusted remote desktop server could exploit this vulnerability. This makes it a high-risk issue for environments where users connect to multiple remote servers or where server compromise is a realistic threat.
The remediation for CVE-2020-11047 involves upgrading to FreeRDP version 2.0.0 or later, where the vulnerability has been patched through proper input validation and bounds checking in the autodetect_recv_bandwidth_measure_results function. Security practitioners should implement immediate patch management procedures to address this vulnerability across all affected systems. Additionally, network segmentation and server authentication mechanisms should be strengthened to prevent unauthorized server access that could lead to exploitation. Organizations should also consider implementing monitoring for unusual bandwidth measurement traffic patterns that might indicate exploitation attempts, as this vulnerability can be leveraged to perform reconnaissance activities without requiring direct system compromise.
This vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol usage and demonstrates how seemingly benign network protocols can be weaponized for memory disclosure attacks. The patch implemented in version 2.0.0 specifically addresses the insufficient bounds checking by validating input lengths before processing measurement results, preventing the out-of-bounds memory access that previously occurred during the automatic bandwidth detection process.