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Code Execution Vulnerabilities Patched in FreeRDP

Researchers at Cisco’s Talos security intelligence and research group have discovered several potentially serious vulnerabilities in FreeRDP. The tool’s developers patched the flaws on Monday with the release of an update.

FreeRDP is an open-source implementation of Microsoft’s Remote Desktop Protocol (RDP). The software, which allows users to remotely connect to other devices, is included in several Linux distributions and is available for both Windows and Mac systems. The FreeRDP library is also used by many commercial applications.

While FreeRDP is typically used for legitimate purposes, it has also been leveraged by cybercriminals, including the notorious group known as Carbanak and Anunak.

Talos researchers discovered that FreeRDP 2.0.0-beta1 on Windows, Linux and Mac OS X is affected by six vulnerabilities that can be exploited for remote code execution and denial-of-service (DoS) attacks.

The RCE flaws, both tracked as CVE-2017-2834 and assigned a severity rating of “high,” exist due to the use of untrusted data in handling the license authentication and reception of an RDP packet from the server.

“The license message sent by the server contains a length field, which is not correctly verified by FreeRDP. For internal purposes, the library decreases this value by 4, if the server is sent a value inferior to 3, this will result in a negative value and the writing of packet contents outside of the allocated buffer in memory. This vulnerability can allow the execution of arbitrary code on the FreeRDP client side,” Talos said in its advisory.

The DoS vulnerabilities, which allow an attacker to crash the client, exist due to the way the client handles proprietary server certificates, security data, and license challenge packets.

The security holes can be exploited by sending specially crafted packets, either via a man-in-the-middle (MitM) attack or by compromising the server.

Talos has made available technical details and developed proof-of-concept (PoC) exploits for the vulnerabilities.

The flaws were patched with the release of FreeRDP 2.0.0-rc0 on Monday. FreeRDP developers have also published an advisory pinpointing the changes made to the code.

Related: Cisco Talos Extends Vulnerability Disclosure Timeline

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.