CVE-1999-0737 in IIS
Summary
by MITRE
The viewcode.asp sample file in IIS and Site Server allows remote attackers to read arbitrary files.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-0737 represents a critical security flaw in Microsoft Internet Information Services and Microsoft Site Server implementations. This issue affects the viewcode.asp sample file which was included as part of the default installation packages for these web server products. The vulnerability stems from insufficient input validation and access control mechanisms within the sample file, allowing malicious actors to exploit a path traversal flaw that enables arbitrary file reading capabilities. The flaw exists in the way the sample file processes user-supplied input parameters, particularly when handling file path requests, which creates an opportunity for remote attackers to access sensitive system files that should normally be restricted from public viewing.
The technical nature of this vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. This weakness allows attackers to access files and directories that are stored outside the intended directory, typically by manipulating input data to include directory path characters such as ../ or ..\ sequences. In the context of IIS and Site Server, the viewcode.asp sample file was designed to display source code of other ASP files for demonstration purposes, but due to improper parameter validation, it failed to restrict file access to only authorized files. Attackers could leverage this by crafting malicious URLs that included path traversal sequences, thereby bypassing normal file access controls and gaining access to system files, configuration files, or even source code of other applications running on the same server.
The operational impact of CVE-1999-0737 extends far beyond simple information disclosure. When exploited, this vulnerability allows attackers to read arbitrary files from the target system, potentially exposing sensitive information such as database connection strings, user credentials stored in configuration files, source code of proprietary applications, and system configuration details. The implications are particularly severe in enterprise environments where IIS and Site Server were commonly deployed, as these servers often host critical business applications and contain sensitive corporate data. The vulnerability essentially provides attackers with a backdoor method to explore the file system and extract valuable information that could be used for further exploitation, including privilege escalation attacks, credential harvesting, or reconnaissance for more sophisticated attacks. This type of vulnerability directly relates to the ATT&CK technique T1083, which covers directory and file permissions enumeration, and T1566, which covers spearphishing with a link, as attackers could use this vulnerability to gather intelligence before launching more targeted attacks.
The mitigation strategies for this vulnerability primarily focus on immediate remediation through software updates and configuration changes. Microsoft released patches for this vulnerability as part of their regular security updates, and organizations should ensure they have applied the appropriate security fixes for their IIS and Site Server versions. Additionally, administrators should remove or disable the viewcode.asp sample file from production environments, as it was only intended for demonstration purposes and poses unnecessary security risks when deployed in live systems. Network segmentation and access control measures should be implemented to limit access to sensitive server functionality, and web application firewalls can provide additional protection against path traversal attempts. The vulnerability serves as a classic example of why proper input validation and principle of least privilege access controls are essential security measures, and it highlights the importance of regularly reviewing and removing unnecessary sample files and demonstration code from production systems to minimize attack surface exposure.