CVE-2017-6465 in FTPshell Client
Summary
by MITRE
Remote Code Execution was discovered in FTPShell Client 6.53. By default, the client sends a PWD command to the FTP server it is connecting to; however, it doesn't check the response's length, leading to a buffer overflow situation.
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Analysis
by VulDB Data Team • 06/15/2024
The vulnerability identified as CVE-2017-6465 represents a critical remote code execution flaw in FTPShell Client version 6.53, demonstrating a classic buffer overflow condition that can be exploited by remote attackers to gain unauthorized system access. This vulnerability specifically affects the client-side application's handling of FTP server responses during the connection process, where the software fails to properly validate the length of responses received from the remote server. The issue manifests when the client sends a PWD (Print Working Directory) command to the FTP server as part of its normal operation, which is a standard command used to retrieve the current working directory on the remote server. The flaw occurs in the client's response processing logic where it does not adequately check the size of the server's response before attempting to store it in a fixed-size buffer, creating an exploitable condition that allows attackers to overwrite adjacent memory locations.
The technical implementation of this vulnerability stems from poor input validation practices within the FTPShell Client's network communication handling code, which aligns with CWE-121, CWE-122, and CWE-787 categories related to buffer overflow conditions. When an attacker controls the FTP server to which the vulnerable client connects, they can craft a malicious response to the PWD command that exceeds the allocated buffer size, causing a stack-based buffer overflow that can be leveraged to execute arbitrary code on the victim's system. This type of vulnerability falls under the ATT&CK technique T1059.007 for Command and Scripting Interpreter, as successful exploitation would enable attackers to execute commands on the compromised system. The buffer overflow occurs because the client application does not implement proper bounds checking on the server response length, allowing an attacker to inject malicious data that overflows the designated memory buffer and potentially overwrite critical program execution pointers or return addresses.
The operational impact of this vulnerability extends beyond simple remote code execution, as it represents a significant threat to organizations that rely on FTPShell Client for file transfer operations and system administration tasks. The vulnerability can be exploited from anywhere on the internet, making it particularly dangerous for organizations that maintain open FTP connections or use the client in environments where attackers can control or influence FTP servers. Attackers exploiting this vulnerability could gain full system control, potentially leading to data breaches, system compromise, and further lateral movement within network environments. The flaw affects the confidentiality, integrity, and availability of systems using the vulnerable client, as unauthorized parties could execute malicious code, modify system files, or disrupt normal operations. Organizations using FTPShell Client 6.53 are particularly at risk because the vulnerability exists in the default configuration, requiring no special conditions or user interaction beyond establishing a normal FTP connection to the vulnerable client.
Mitigation strategies for CVE-2017-6465 should focus on immediate patching of the vulnerable software, as the vendor has likely released updates addressing this specific buffer overflow condition. System administrators should also implement network segmentation and access controls to limit exposure of systems running the vulnerable client, particularly those that connect to untrusted FTP servers. Additional protective measures include implementing network monitoring to detect unusual FTP traffic patterns that might indicate exploitation attempts, configuring firewalls to restrict FTP connections to trusted servers only, and employing intrusion detection systems that can identify potential buffer overflow exploitation attempts. Organizations should also consider migrating to more secure FTP alternatives such as SFTP or FTPS, which provide encryption and better input validation mechanisms that reduce the risk of similar buffer overflow conditions. The vulnerability demonstrates the importance of proper input validation and bounds checking in client applications, particularly those handling network communications where external inputs can be manipulated by attackers to cause memory corruption and system compromise.