CVE-2016-20046 in zFTP
Summary
by MITRE • 03/28/2026
zFTP Client 20061220+dfsg3-4.1 contains a buffer overflow vulnerability in the NAME parameter handling of FTP connections that allows local attackers to crash the application or execute arbitrary code. Attackers can supply an oversized NAME value exceeding the 80-byte buffer allocated in strcpy_chk to overwrite the instruction pointer and execute shellcode with user privileges.
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Analysis
by VulDB Data Team • 05/06/2026
The vulnerability identified as CVE-2016-20046 represents a critical buffer overflow flaw within the zFTP Client software version 20061220+dfsg3-4.1. This issue stems from inadequate input validation during FTP connection processing specifically when handling the NAME parameter. The flaw manifests in the application's failure to properly bounds-check user-supplied data before copying it into a statically allocated 80-byte buffer. The vulnerability is classified as a classic stack-based buffer overflow that occurs when the strcpy_chk function is invoked with an oversized input string, leading to memory corruption that can be exploited by malicious actors.
The technical implementation of this vulnerability follows established patterns found in CWE-121 Stack-based Buffer Overflow, where insufficient bounds checking allows attackers to overwrite adjacent memory locations including the instruction pointer or return addresses. In the context of zFTP Client, when an attacker supplies a NAME parameter exceeding 80 characters, the vulnerable code path executes strcpy_chk without proper validation, causing a buffer overflow that corrupts the stack frame. This memory corruption can be manipulated to redirect program execution flow, enabling attackers to execute arbitrary code with the privileges of the user running the application. The vulnerability is particularly concerning as it requires no special privileges beyond local access, making it a local privilege escalation vector.
The operational impact of CVE-2016-20046 extends beyond simple application crashes to potential full system compromise when the target system has elevated privileges. Attackers can leverage this vulnerability to execute malicious shellcode, potentially gaining unauthorized access to sensitive data or establishing persistent backdoors within the system. The vulnerability affects systems running the specific version of zFTP Client mentioned, and the exploitation process follows typical attack patterns documented in MITRE ATT&CK framework under techniques such as T1059 Command and Scripting Interpreter and T1068 Exploitation for Privilege Escalation. The local nature of the attack means that an attacker must already have access to the system, but the privilege escalation aspect could allow them to move laterally within a network or escalate to higher-privilege accounts.
Mitigation strategies for CVE-2016-20046 should prioritize immediate software updates to the latest available version of zFTP Client that addresses the buffer overflow vulnerability. System administrators should implement proper input validation measures and consider deploying application whitelisting solutions to prevent exploitation attempts. The vulnerability demonstrates the importance of secure coding practices including bounds checking, use of safe string handling functions, and proper memory management. Additionally, network segmentation and privilege separation can reduce the potential impact of successful exploitation attempts. Organizations should also implement regular security audits and vulnerability assessments to identify similar issues in legacy applications that may not receive ongoing security updates, as this vulnerability represents a common class of flaws that continues to appear in older software implementations.