CVE-2017-18047 in nfsAxe
Summary
by MITRE
Buffer Overflow in the FTP client in LabF nfsAxe 3.7 allows remote FTP servers to execute arbitrary code via a long reply.
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Analysis
by VulDB Data Team • 12/26/2019
The vulnerability CVE-2017-18047 represents a critical buffer overflow flaw within the File Transfer Protocol client component of LabF nfsAxe version 3.7. This security defect resides in the client-side implementation that processes responses from remote FTP servers, creating a potential pathway for remote code execution attacks. The vulnerability specifically manifests when the client receives a malformed FTP server reply containing excessive data that exceeds the allocated buffer size, leading to memory corruption that can be exploited by malicious actors. The flaw demonstrates characteristics consistent with CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. This vulnerability operates at the application layer and affects the FTP client functionality specifically, making it a targeted attack vector against systems that rely on nfsAxe for network file operations. The exploitation of this vulnerability enables remote attackers to execute arbitrary code on the victim system with the privileges of the user running the nfsAxe application, potentially leading to complete system compromise and unauthorized access to network resources.
The technical implementation of this buffer overflow occurs during the processing of FTP server responses where the client application fails to properly validate the length of incoming data before copying it into a fixed-size buffer. When an FTP server sends a response containing more data than the allocated buffer space, the excess data overflows into adjacent memory regions, potentially overwriting critical program variables, return addresses, or function pointers. This memory corruption can be carefully manipulated to redirect program execution flow, allowing attackers to inject and execute malicious code within the context of the nfsAxe application. The vulnerability aligns with ATT&CK technique T1203, which involves the exploitation of software vulnerabilities to gain code execution, and demonstrates how improper input validation can create opportunities for privilege escalation attacks. The buffer overflow specifically affects the FTP client's response parsing logic, where the application does not implement adequate bounds checking or input sanitization mechanisms to handle unexpected data lengths from remote servers.
The operational impact of CVE-2017-18047 extends beyond simple data corruption, as it creates a persistent security risk for organizations relying on nfsAxe for file sharing operations. Systems using this software become vulnerable to remote exploitation without requiring any user interaction or authentication, making the attack surface particularly dangerous in networked environments. The vulnerability can be exploited by any remote FTP server that the victim system attempts to connect to, including compromised servers or those under the control of malicious actors. This makes the attack vector particularly effective for lateral movement within networks where systems may be configured to connect to multiple FTP servers automatically. The potential for privilege escalation exists because the nfsAxe application typically runs with elevated privileges to perform file operations, meaning successful exploitation could provide attackers with administrative access to the compromised system. Organizations may face significant operational disruption as attackers could use this vulnerability to establish persistent access, exfiltrate sensitive data, or deploy additional malware within the network infrastructure.
Mitigation strategies for CVE-2017-18047 require immediate action to address the buffer overflow vulnerability through software updates and operational controls. The primary recommendation involves upgrading to a patched version of LabF nfsAxe that includes proper bounds checking and input validation mechanisms to prevent buffer overflows during FTP response processing. Organizations should also implement network segmentation and firewall rules to limit exposure to untrusted FTP servers, particularly in environments where automatic FTP connections are configured. Additional defensive measures include monitoring network traffic for suspicious FTP server responses that may indicate exploitation attempts, implementing application whitelisting to restrict execution of unauthorized code, and conducting regular vulnerability assessments to identify similar flaws in other network applications. The vulnerability demonstrates the importance of proper software security practices including input validation, memory safety mechanisms, and regular security updates. Organizations should also consider implementing intrusion detection systems that can identify and alert on potential exploitation attempts targeting similar buffer overflow vulnerabilities, as these attacks often follow predictable patterns that can be detected through network traffic analysis and behavioral monitoring.