CVE-2004-0173 in HTTP Server
Summary
by MITRE
Directory traversal vulnerability in Apache 1.3.29 and earlier, and Apache 2.0.48 and earlier, when running on Cygwin, allows remote attackers to read arbitrary files via a URL containing "..%5C" (dot dot encoded backslash) sequences.
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Analysis
by VulDB Data Team • 08/21/2025
This directory traversal vulnerability exists in Apache web servers version 1.3.29 and earlier, as well as Apache 2.0.48 and earlier, specifically when deployed on Cygwin operating systems. The flaw stems from improper input validation of URL paths that allows attackers to manipulate file access requests through specially crafted URL sequences. The vulnerability exploits the difference in how Cygwin handles backslash characters compared to standard unix-like systems, creating a path traversal opportunity that bypasses normal security controls. The specific attack vector involves using "..%5C" sequences in URLs where %5C represents the encoded backslash character, enabling attackers to navigate outside the intended document root directory and access arbitrary files on the server.
The technical implementation of this vulnerability relies on the inconsistent handling of directory traversal sequences between Windows-style and Unix-style path resolution mechanisms. In Cygwin environments, the web server fails to properly normalize path components when processing URL requests containing encoded backslash sequences, allowing the traversal logic to interpret these sequences as legitimate navigation commands rather than malicious input. This creates a path traversal condition where the server processes requests like "/etc/passwd" or other sensitive files that should be protected from external access. The vulnerability is classified as CWE-22 according to the Common Weakness Enumeration, which specifically addresses improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal.
The operational impact of this vulnerability is significant as it provides remote attackers with unauthorized access to sensitive system files that could contain critical information such as user credentials, system configurations, application data, and other confidential information. Attackers can leverage this vulnerability to read files that are normally protected by the web server's security model, potentially leading to complete system compromise. The vulnerability affects not only basic file access but can also expose configuration files that might contain database passwords, API keys, or other sensitive credentials. According to MITRE ATT&CK framework, this vulnerability maps to T1083 (File and Directory Discovery) and T1566 (Phishing with Malicious Attachment) as attackers can use this access to gather intelligence for further attacks.
Mitigation strategies for this vulnerability include immediate patching of Apache installations to versions that properly handle path traversal sequences on Cygwin systems. Administrators should ensure that all Apache installations are updated to versions that properly normalize and validate URL path components regardless of the underlying operating system platform. Additional protective measures include implementing proper input validation at the web server level, configuring restrictive directory permissions, and deploying web application firewalls that can detect and block suspicious path traversal attempts. Organizations should also conduct regular security assessments to identify and remediate similar vulnerabilities in other web applications and services. The vulnerability demonstrates the importance of platform-specific security considerations when deploying web servers in mixed operating environments, particularly where cross-platform compatibility issues can create unexpected security gaps.