CVE-2017-2838 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 identified as CVE-2017-2838 represents a critical denial of service flaw within the FreeRDP 2.0.0-beta1+android11 implementation that specifically targets the challenge packet handling mechanism. This issue falls under the category of improper input validation and memory safety concerns, with the vulnerability being classified as a CWE-125 out-of-bounds read or CWE-476 null pointer dereference depending on the specific implementation details. The flaw manifests when the RDP client processes specially crafted challenge packets that contain malformed data structures or unexpected values in the challenge response sequence.
FreeRDP serves as an open-source Remote Desktop Protocol implementation that enables users to connect to Windows servers and other RDP-compatible systems from various platforms including Linux, macOS, and Android devices. The vulnerability occurs during the initial authentication handshake process where the client receives challenge packets from the server to establish secure communication channels. These challenge packets typically contain cryptographic parameters and session identifiers that are essential for the RDP security framework. The flaw exists in how the software processes these packets without adequate bounds checking or error handling for malformed inputs.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable more sophisticated attacks including man-in-the-middle scenarios. When an attacker successfully triggers this denial of service condition, the FreeRDP client terminates unexpectedly, rendering the connection unusable and preventing legitimate users from accessing the target system. This vulnerability affects systems where FreeRDP is deployed as a client application, particularly in enterprise environments where remote desktop connections are frequently used for administrative tasks and user access. The attack vector requires minimal privileges as the vulnerability can be exploited through network-based interactions without requiring authentication to the target system.
The technical exploitation of this vulnerability aligns with ATT&CK technique T1499.004 for network denial of service and potentially T1566.001 for initial access through network service exploitation. The flaw demonstrates poor defensive programming practices where the software fails to implement proper input sanitization and exception handling for network protocols. Organizations utilizing FreeRDP in their infrastructure should consider implementing network segmentation and monitoring to detect potential exploitation attempts. The vulnerability also highlights the importance of proper code review and security testing for protocol implementations, particularly those handling cryptographic handshake sequences. Mitigation strategies include upgrading to patched versions of FreeRDP, implementing network-based access controls, and deploying intrusion detection systems to monitor for suspicious challenge packet patterns. The issue underscores the need for robust error handling in security-sensitive applications and demonstrates how seemingly minor input validation gaps can lead to complete service disruption.
This vulnerability represents a fundamental flaw in the RDP client implementation that affects the broader remote desktop ecosystem and emphasizes the critical importance of secure protocol handling in enterprise security infrastructure. The lack of proper bounds checking in challenge packet processing creates a pathway for attackers to disrupt legitimate business operations and potentially gain unauthorized access to systems through service disruption attacks. Organizations should prioritize patch management for FreeRDP installations and consider alternative remote access solutions if immediate upgrades are not feasible. The vulnerability also serves as a reminder of the importance of thorough security testing for open source components that are widely deployed in enterprise environments and the need for continuous monitoring of security advisories for all software dependencies.