CVE-1999-1544 in IIS
Summary
by MITRE
Buffer overflow in FTP server in Microsoft IIS 3.0 and 4.0 allows local and sometimes remote attackers to cause a denial of service via a long NLST (ls) command.
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Analysis
by VulDB Data Team • 06/23/2021
The vulnerability identified as CVE-1999-1544 represents a critical buffer overflow flaw within the File Transfer Protocol server component of Microsoft Internet Information Services versions 3.0 and 4.0. This issue arises specifically when processing the NLST command, which is used to list directory contents in FTP protocol implementations. The flaw exists at the core level of IIS's FTP service handling mechanism, where insufficient input validation allows maliciously crafted data to exceed allocated buffer boundaries. The vulnerability classifies under CWE-121 as a stack-based buffer overflow, indicating that the overflow occurs in stack memory allocated for function parameters and local variables during program execution. This type of vulnerability is particularly dangerous because it can lead to arbitrary code execution or system instability when exploited.
The technical implementation of this vulnerability stems from the FTP server's failure to properly validate the length of input data provided in NLST commands. When an attacker sends a specially crafted command containing an excessive number of characters, the server's buffer allocation mechanism cannot accommodate the data, causing memory corruption. The attack can be executed locally through direct system access or remotely by connecting to the FTP service over the network. The remote exploitation capability significantly broadens the attack surface, making this vulnerability particularly concerning for publicly accessible web servers. The buffer overflow occurs during command processing where the FTP service attempts to store the directory listing response in a fixed-size memory buffer without proper bounds checking, directly violating secure coding practices recommended by the OWASP Top Ten and CERT/CC secure coding guidelines.
The operational impact of CVE-1999-1544 extends beyond simple denial of service conditions to potentially enable more severe compromise scenarios. While the primary effect manifests as service disruption, the buffer overflow condition creates opportunities for attackers to execute arbitrary code on vulnerable systems. This vulnerability directly maps to ATT&CK technique T1210 which involves exploiting buffer overflow vulnerabilities to gain unauthorized access or escalate privileges. The affected IIS versions were widely deployed in enterprise environments during the late 1990s, making this vulnerability a significant threat to organizations relying on Microsoft's web server solutions. System administrators faced the challenge of determining whether the overflow would result in immediate service disruption or provide a foothold for more sophisticated attacks, as the memory corruption could potentially be leveraged to overwrite critical program execution pointers or return addresses.
Mitigation strategies for this vulnerability required immediate patching of affected IIS installations through Microsoft security updates, as the original code base contained fundamental design flaws in input handling. Organizations should have implemented network segmentation to limit access to FTP services, particularly disabling unnecessary FTP functionality on web servers. The recommended approach involved applying Microsoft Security Bulletin MS99-045 which provided the necessary code modifications to properly validate NLST command inputs and prevent buffer overflows. Additionally, implementing intrusion detection systems capable of identifying suspicious FTP command patterns and configuring firewall rules to restrict FTP access to trusted networks helped reduce exploitation risk. The vulnerability highlighted the importance of input validation and memory safety practices in server applications, influencing subsequent security development lifecycle requirements for Microsoft and other software vendors. Organizations were advised to conduct comprehensive vulnerability assessments to identify all instances of affected IIS installations and ensure proper patch management procedures were in place to prevent similar issues from arising in future deployments.