CVE-2000-1090 in IIS
Summary
by MITRE
Microsoft IIS for Far East editions 4.0 and 5.0 allows remote attackers to read source code for parsed pages via a malformed URL that uses the lead-byte of a double-byte character.
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Analysis
by VulDB Data Team • 04/07/2019
Microsoft IIS for Far East editions version 4.0 and 5.0 contained a critical vulnerability that allowed remote attackers to access source code files through malformed URL requests utilizing double-byte character sequences. This vulnerability specifically affected servers configured to handle Far East character sets including Japanese, Chinese, and Korean languages where double-byte character encoding is standard. The flaw occurred within the URL parsing mechanism when the web server encountered lead bytes from double-byte character sets in malformed URLs, causing the server to misinterpret the request and potentially expose server-side source code files. This represents a classic path traversal vulnerability that falls under CWE-22 Path Traversal and aligns with ATT&CK technique T1213.002 Data from Information Repositories. The vulnerability exploited the server's handling of multi-byte character sequences where a malformed URL containing a lead byte from a double-byte character could cause the IIS web server to process the request incorrectly, potentially leading to source code disclosure. The issue was particularly severe because it allowed attackers to retrieve sensitive source code files that could contain database connection strings, application logic, and other confidential information. Attackers could craft URLs that appeared legitimate to the web server but contained malformed double-byte sequences that would trigger the source code disclosure behavior. This vulnerability had significant operational impact as it could be exploited without authentication and provided attackers with access to application source code that could be used for further exploitation. The problem was compounded by the fact that the vulnerability only affected Far East editions of IIS, making it more targeted but still potentially devastating for organizations using these specific server configurations. Organizations running these vulnerable versions of IIS were at risk of exposure to source code disclosure attacks that could lead to complete application compromise. The vulnerability demonstrated the complexity of handling international character sets in web server implementations and highlighted the importance of proper input validation in multi-byte character environments. Security patches and updates were required to address the parsing logic that incorrectly handled double-byte character lead bytes in URL requests. The remediation involved updating the IIS server software to versions that properly validated URL inputs and correctly handled multi-byte character sequences without exposing source code files. This vulnerability underscored the need for comprehensive testing of international character set handling in web applications and the potential security implications of improper input validation in server-side processing. The issue also highlighted the importance of following secure coding practices and proper error handling when processing user-supplied data in web applications that must handle multiple character encodings. Organizations should have implemented immediate patching procedures and enhanced monitoring for suspicious URL requests containing malformed double-byte sequences to prevent exploitation of this vulnerability.