CVE-1999-0450 in IIS
Summary
by MITRE
In IIS, an attacker could determine a real path using a request for a non-existent URL that would be interpreted by Perl (perl.exe).
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Analysis
by VulDB Data Team • 10/26/2025
This vulnerability exists within Microsoft Internet Information Services version 3.0 and 4.0 where the web server fails to properly handle requests for non-existent URLs that contain perl.exe references. When an attacker submits a request for a non-existent URL that includes perl.exe in the path, the server attempts to execute the perl interpreter and returns detailed error messages that reveal the actual physical path structure of the web server. The flaw stems from the server's inadequate input validation and improper error handling mechanisms that allow the perl.exe interpreter to be invoked with user-supplied data without proper sanitization.
The technical exploitation occurs through simple HTTP requests that contain perl.exe references in the URL path, causing the IIS server to attempt execution of the perl interpreter and subsequently return detailed error messages containing the actual file system paths. This represents a path disclosure vulnerability that can be categorized under CWE-200 Information Exposure Through an Error Message, where the system inadvertently reveals sensitive information about its internal structure. The vulnerability allows attackers to map the physical directory structure of the web server, which can be leveraged for further attacks including directory traversal, file inclusion, or privilege escalation attempts.
The operational impact of this vulnerability is significant as it provides attackers with critical information about the server's file system layout that can be used for subsequent exploitation phases. The disclosed paths may reveal sensitive directory structures including administrative areas, configuration files, or other system components that could be targeted for further compromise. This vulnerability aligns with ATT&CK technique T1083 Directory and File System Discovery, as it enables adversaries to gather information about the target system's file structure. The exposure of physical paths can facilitate more sophisticated attacks such as local file inclusion vulnerabilities or help attackers craft more effective payloads for exploitation of other system weaknesses.
Organizations should implement immediate mitigations including disabling perl.exe execution on the web server, configuring proper error handling to prevent detailed error messages from being returned to clients, and implementing input validation controls that filter out suspicious URL patterns containing executable references. The recommended approach involves configuring IIS to return generic error messages instead of detailed system information, restricting perl.exe execution through web server configuration, and applying the appropriate security patches from Microsoft that address this specific vulnerability. Additionally, network-based intrusion detection systems should be configured to monitor for requests containing perl.exe references as potential indicators of exploitation attempts.