CVE-2020-11099 in FreeRDP
Summary
by MITRE
In FreeRDP before version 2.1.2, there is an out of bounds read in license_read_new_or_upgrade_license_packet. A manipulated license packet can lead to out of bound reads to an internal buffer. This is fixed in version 2.1.2.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/19/2025
The vulnerability identified as CVE-2020-11099 represents a critical out-of-bounds read flaw in the FreeRDP remote desktop protocol implementation that affects versions prior to 2.1.2. This issue resides within the license_read_new_or_upgrade_license_packet function, which processes license packets during the RDP connection establishment phase. The vulnerability stems from inadequate input validation and boundary checking when parsing license information transmitted between RDP client and server components. Attackers can exploit this weakness by crafting malicious license packets that trigger memory access violations, potentially leading to information disclosure or system instability. The flaw manifests as an out-of-bounds read operation that accesses internal buffer memory beyond its allocated boundaries, creating opportunities for exploitation that align with CWE-125, which specifically addresses out-of-bounds read vulnerabilities.
The technical execution of this vulnerability occurs during the RDP license negotiation process where FreeRDP receives and processes license information from remote servers. When the license_read_new_or_upgrade_license_packet function encounters malformed input, it fails to properly validate the packet structure before attempting to read from internal buffers. This allows an attacker positioned within the network or able to intercept RDP traffic to craft specially designed license packets that cause the application to read memory locations that are not part of the intended buffer. The vulnerability's impact extends beyond simple memory access violations as it can potentially expose sensitive information from the application's memory space, including cryptographic keys, session data, or other confidential information. This type of vulnerability is particularly concerning in RDP implementations as it can be leveraged to escalate privileges or gain unauthorized access to systems.
The operational impact of CVE-2020-11099 is significant for organizations relying on FreeRDP for remote desktop connectivity, particularly in enterprise environments where RDP is commonly used for administrative access and remote work solutions. The vulnerability creates a potential attack vector that could be exploited by threat actors to compromise systems during the initial connection phase, before authentication mechanisms fully engage. Organizations using FreeRDP versions prior to 2.1.2 face increased risk of information disclosure and potential system compromise, especially when connecting to untrusted RDP servers or when network traffic is not properly secured. The vulnerability's exploitation requires minimal network access and can be automated, making it particularly dangerous in environments where RDP is exposed to the internet or where network segmentation is insufficient. This aligns with ATT&CK technique T1021.001 which covers remote services and credential access through RDP protocols.
Mitigation strategies for CVE-2020-11099 focus primarily on upgrading to FreeRDP version 2.1.2 or later, which includes proper input validation and boundary checking mechanisms. Organizations should implement network segmentation to limit RDP access to trusted networks and consider deploying additional network monitoring to detect suspicious license packet traffic patterns. Security teams should also ensure that all RDP implementations are regularly updated and patched according to vendor advisories. Additional defensive measures include implementing strict network access controls, using VPNs for RDP access, and monitoring for unusual connection patterns that might indicate exploitation attempts. The fix implemented in version 2.1.2 addresses the root cause by adding proper validation of license packet structures before buffer access operations, preventing the out-of-bounds read conditions that previously allowed attackers to exploit the vulnerability.