CVE-1999-1539 in QVT Term Plus
Summary
by MITRE
Buffer overflow in FTP server in QPC Software's QVT/Term Plus versions 4.2d and 4.3 and QVT/Net 4.3 allows remote attackers to cause a denial of service, and possibly execute arbitrary commands, via a long (1) user name or (2) password.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-1539 represents a critical buffer overflow flaw affecting FTP servers within QPC Software's QVT/Term Plus versions 4.2d and 4.3, as well as QVT/Net 4.3 products. This security weakness stems from inadequate input validation mechanisms within the authentication process of these legacy FTP implementations, creating a pathway for malicious actors to exploit the software through carefully crafted user credentials. The vulnerability specifically targets the handling of user name and password inputs, where the software fails to properly validate the length of these authentication parameters before processing them in memory buffers.
The technical nature of this flaw aligns with CWE-121, which describes stack-based buffer overflow conditions that occur when a program writes data beyond the boundaries of a fixed-length buffer. In this case, the overflow manifests during FTP authentication when attackers supply excessively long user name or password strings that exceed the allocated buffer space. The implementation lacks proper bounds checking and input sanitization, allowing the overflow to overwrite adjacent memory locations including return addresses, function pointers, and other critical control data structures. This type of vulnerability falls under the broader category of CWE-787, heap-based buffer overflows, when the software uses dynamic memory allocation without adequate size verification.
The operational impact of this vulnerability extends beyond simple denial of service conditions, presenting potential for remote code execution in the target system. When the buffer overflow occurs, it can cause the FTP service to crash and restart, resulting in denial of service for legitimate users attempting to access the system. However, more sophisticated attackers may exploit the memory corruption to inject and execute malicious code with the privileges of the FTP service account, potentially leading to complete system compromise. The vulnerability affects the availability and integrity of the network services, as well as the confidentiality of data transmitted through the compromised FTP server. Attackers leveraging this weakness can leverage the control flow corruption to redirect program execution to malicious payloads, particularly when the FTP service runs with elevated privileges.
Mitigation strategies for this vulnerability require immediate attention through software updates and patches provided by QPC Software, as well as network-level defensive measures. Organizations should implement input validation controls at multiple layers including network firewalls, intrusion detection systems, and application-level protections to prevent excessively long authentication strings from reaching the vulnerable FTP service. The implementation of proper bounds checking and input sanitization within the FTP server code represents the fundamental fix required to address the underlying buffer overflow condition. Security practitioners should also consider implementing network segmentation to isolate FTP services and limit the potential attack surface, while monitoring for suspicious authentication attempts that may indicate exploitation attempts. This vulnerability demonstrates the critical importance of input validation and memory safety practices in network service implementations, aligning with ATT&CK technique T1190 for exploitation of vulnerabilities and T1499 for denial of service attacks. The remediation process should include comprehensive testing to ensure that patch implementations do not introduce regressions in legitimate FTP service functionality while maintaining the security hardening necessary to prevent similar buffer overflow conditions in other software components.