CVE-1999-0253 in IIS
Summary
by MITRE
iis 3.0 with the iis-fix hotfix installed allows remote intruders to read source code for asp programs by using a %2e instead of a . (dot) in the url.
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Analysis
by VulDB Data Team • 06/23/2021
The vulnerability described in CVE-1999-0253 represents a critical directory traversal flaw affecting Internet Information Services version 3.0 when patched with the iis-fix hotfix. This issue stems from improper input validation within the web server's handling of uniform resource locators, specifically in how it processes encoded characters within file paths. The vulnerability exploits a fundamental weakness in path resolution mechanisms that fail to properly sanitize or normalize URL-encoded sequences, creating an avenue for unauthorized access to server-side resources.
The technical exploitation occurs through the manipulation of URL encoding where attackers substitute the standard dot character with its hexadecimal representation %2e. This seemingly innocuous character replacement bypasses normal path validation checks and allows malicious users to traverse directory structures beyond intended access boundaries. When the iis-fix hotfix was applied, it inadvertently introduced a regression that failed to properly handle this specific encoding pattern, creating a security loophole that persisted despite the patch intended to address other vulnerabilities. The flaw operates at the application layer of the osi model, specifically within the web server's request processing pipeline where URL normalization should occur before file access decisions are made.
The operational impact of this vulnerability extends far beyond simple information disclosure, as it enables attackers to access sensitive source code files containing database connection strings, authentication credentials, application logic, and business-critical information. Asp programs often contain embedded database credentials, proprietary algorithms, and system configuration details that could be leveraged for further attacks. The vulnerability affects the confidentiality aspect of the cia triad by allowing unauthorized data access, potentially leading to complete system compromise if sensitive information is exposed. This type of vulnerability directly aligns with attack patterns documented in the attack pattern taxonomy under path traversal techniques and represents a common weakness identified in the software security domain.
Organizations affected by this vulnerability should immediately implement multiple layers of mitigation strategies including web application firewalls that can detect and block encoded character sequences, proper input validation at all application interfaces, and comprehensive security testing of url handling mechanisms. The fix requires either rolling back the problematic iis-fix hotfix and applying a proper security patch, or implementing custom URL normalization rules within the web server configuration. This vulnerability demonstrates the importance of thorough regression testing when applying security patches and highlights the need for organizations to maintain current security baselines that include proper path validation. Compliance with industry standards such as owasp top ten and nist cybersecurity framework requires implementing proper input sanitization and access control mechanisms that prevent directory traversal attacks.
The vulnerability classification aligns with common weakness enumeration cwes 22 and 77, which specifically address path traversal and improper input validation issues respectively. From an attack perspective, this vulnerability maps to techniques in the attack tree methodology where path traversal represents a foundational attack vector that can lead to privilege escalation, data exfiltration, and system compromise. The security implications extend beyond immediate code access to potential exploitation of other vulnerabilities within the same application stack, making this a critical concern for organizations maintaining legacy iis 3.0 environments. Proper security awareness training for developers and system administrators should emphasize the importance of validating all user-supplied input and understanding how different encoding schemes can bypass security controls.