CVE-2001-0053 in NetBSD
Summary
by MITRE
One-byte buffer overflow in replydirname function in BSD-based ftpd allows remote attackers to gain root privileges.
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Analysis
by VulDB Data Team • 10/10/2025
The vulnerability described in CVE-2001-0053 represents a critical buffer overflow flaw within the ftpd daemon implementation on BSD-based systems. This specific issue occurs within the replydirname function, which handles directory name responses during ftp protocol operations. The flaw manifests as a one-byte buffer overflow, indicating that the software writes one byte beyond the allocated buffer space when processing directory names. Such a vulnerability is particularly dangerous because it can be exploited by remote attackers to execute arbitrary code with elevated privileges, potentially leading to complete system compromise.
The technical nature of this vulnerability aligns with CWE-121, which categorizes stack-based buffer overflow conditions, and specifically demonstrates how improper input validation can lead to memory corruption. The ftpd daemon, being a fundamental network service, provides an attractive target for attackers seeking persistent system access. When the replydirname function processes directory names without adequate bounds checking, it creates an opportunity for malicious input to overwrite adjacent memory locations, potentially including return addresses or other critical program state information. This memory corruption can be leveraged to redirect program execution flow and ultimately execute attacker-controlled code.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with a pathway to achieve root access on affected systems. In the context of the ATT&CK framework, this vulnerability maps to the privilege escalation technique where adversaries leverage software flaws to gain elevated system privileges. The attack surface is significant since ftpd services are commonly exposed to external networks, making the vulnerability accessible to remote attackers without requiring local system access. Systems running BSD-based ftpd implementations that have not been patched remain at risk of being compromised, potentially leading to full system takeover, data exfiltration, or use as a launching point for further attacks within a network infrastructure.
Mitigation strategies for this vulnerability require immediate patching of affected ftpd implementations to address the buffer overflow in the replydirname function. Organizations should implement network segmentation to limit exposure of ftp services to untrusted networks, and consider disabling ftp services entirely where possible. Additional defensive measures include implementing intrusion detection systems to monitor for suspicious ftp traffic patterns and conducting regular security audits to identify other potential buffer overflow vulnerabilities in network services. The vulnerability also underscores the importance of input validation and bounds checking in network protocol implementations, as recommended by secure coding practices outlined in various cybersecurity frameworks including those from the SANS Institute and OWASP.