CVE-2017-2839 in FreeRDP
Summary
by MITRE
An exploitable denial of service vulnerability exists within the handling of challenge packets in FreeRDP 2.0.0-beta1+android11. A specially crafted challenge packet can cause the program termination leading to a denial of service condition. An attacker can compromise the server or use man in the middle to trigger this vulnerability.
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Analysis
by VulDB Data Team • 03/07/2023
The vulnerability described in CVE-2017-2839 represents a critical denial of service flaw within the FreeRDP implementation that affects version 2.0.0-beta1+android11. This issue specifically targets the challenge packet handling mechanism that forms a fundamental component of the Remote Desktop Protocol communication framework. The vulnerability stems from inadequate input validation and error handling within the RDP protocol stack, where the software fails to properly process malformed challenge packets that are part of the authentication handshake process. The flaw allows an attacker to craft malicious challenge packets that, when processed by the vulnerable FreeRDP client or server, trigger an abrupt termination of the application. This behavior constitutes a classic buffer overflow or memory corruption scenario where the program's execution flow becomes compromised due to improper handling of unexpected data structures. The vulnerability is particularly concerning because it operates at the protocol level, affecting the core authentication mechanisms that enable secure remote desktop connections.
The technical exploitation of this vulnerability follows a well-established pattern within the realm of network protocol security flaws. The challenge packet in RDP contains cryptographic parameters and server information that must be properly validated before processing. When FreeRDP encounters a specially crafted challenge packet, the parsing logic fails to account for malformed or oversized data fields, leading to memory corruption that ultimately results in program termination. This type of vulnerability falls under the CWE-121 category of stack-based buffer overflow, though it may also manifest as heap corruption depending on the specific implementation details. The attacker can leverage this weakness through various attack vectors including direct network connections to vulnerable servers or by positioning themselves as man-in-the-middle actors in established RDP sessions. The vulnerability's impact extends beyond simple service disruption as it can be used to compromise the integrity of the entire RDP authentication process, potentially enabling more sophisticated attacks.
The operational impact of CVE-2017-2839 creates significant risks for organizations relying on FreeRDP implementations for remote desktop services. The denial of service condition effectively prevents legitimate users from establishing remote connections to affected systems, creating operational disruptions that can span from individual workstation access to enterprise-wide remote work capabilities. In environments where RDP is used for critical infrastructure management, system administrators, or remote support operations, this vulnerability can result in substantial downtime and productivity losses. The attack requires minimal sophistication to execute, making it particularly dangerous as it can be exploited by threat actors with basic networking knowledge. The vulnerability's presence in the android11 variant indicates that mobile RDP clients are also at risk, potentially affecting remote workers who rely on mobile devices for accessing corporate resources. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 (Endpoint Denial of Service) and T1566.001 (Phishing via Social Engineering), as it can be leveraged in both direct service disruption and as part of broader attack chains.
Mitigation strategies for CVE-2017-2839 must address both immediate protection and long-term architectural improvements within FreeRDP implementations. The primary recommendation involves applying the official patches released by the FreeRDP development team that correct the input validation and error handling mechanisms for challenge packet processing. Organizations should implement network-level controls such as firewall rules that restrict RDP traffic to trusted sources and monitor for unusual challenge packet patterns that may indicate exploitation attempts. Additionally, deploying intrusion detection systems capable of identifying malformed RDP packets can provide early warning of potential attacks. The vulnerability highlights the importance of robust input validation practices and proper error handling in protocol implementations, aligning with security best practices outlined in the OWASP Top 10 and NIST SP 800-53 security controls. Regular security assessments of RDP implementations and maintaining updated client and server software versions are essential defensive measures that help prevent exploitation of this and similar vulnerabilities. Organizations should also consider implementing redundant authentication mechanisms and access controls to minimize the impact of potential service disruptions caused by this and other denial of service vulnerabilities.