CVE-1999-0725 in IIS
Summary
by MITRE
When IIS is run with a default language of Chinese, Korean, or Japanese, it allows a remote attacker to view the source code of certain files, a.k.a. "Double Byte Code Page".
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Analysis
by VulDB Data Team • 10/23/2025
This vulnerability exists in Microsoft Internet Information Services when configured with East Asian language support including Chinese, Korean, or Japanese. The flaw stems from how IIS handles double byte character encoding in its file listing and error reporting mechanisms. When a web server responds to requests for directories or files, it uses specific code pages to render content, and the default configuration for these Asian languages creates a condition where source code can be exposed through improper handling of multi-byte character sequences.
The technical implementation of this vulnerability occurs due to a specific code page handling issue in IIS where certain double byte character sequences are not properly escaped or sanitized during web response generation. This allows an attacker to craft malicious requests that exploit the server's interpretation of these character sets to bypass normal access controls and retrieve source code files. The vulnerability is particularly dangerous because it affects the default installation configuration, making it widely exploitable across systems that have not been explicitly hardened.
The operational impact of this vulnerability is significant as it allows remote code execution through source code disclosure, enabling attackers to gain detailed knowledge of web applications and their underlying implementations. This exposure can lead to further exploitation opportunities including identification of application logic flaws, database connection strings, and other sensitive information that could be leveraged for more sophisticated attacks. The vulnerability affects systems running IIS with default language settings for East Asian locales, creating a widespread risk across numerous web servers.
Mitigation strategies include configuring IIS to use appropriate code page settings that properly handle character encoding, disabling directory browsing for sensitive directories, and implementing proper access controls for source code files. Organizations should also consider upgrading to patched versions of IIS, applying the relevant security updates from Microsoft, and implementing network segmentation to limit exposure. This vulnerability aligns with CWE-200, which addresses improper exposure of sensitive information, and represents a classic example of how default configurations can create security weaknesses that align with ATT&CK technique T1566 for initial access through server-side attacks. The issue demonstrates the importance of proper input validation and output encoding in web server implementations and serves as a reminder that default security settings may not be sufficient for production environments.