CWE-29 (路径遍历：’..filename’) — Vulnerability Class 63

CWE-29 represents a critical input validation weakness where software fails to properly sanitize path traversal sequences, specifically the leading backslash-dot-dot notation. Attackers typically exploit this vulnerability by injecting malicious characters into user-supplied input fields, such as file upload forms or URL parameters, to manipulate file system navigation. By appending these sequences to a requested filename, adversaries can escape the intended restricted directory and access sensitive system files, configuration data, or other resources located outside the authorized scope. This unauthorized access can lead to severe data breaches, information disclosure, or remote code execution if the compromised files are executable. To prevent such attacks, developers must rigorously validate and sanitize all user inputs, ensuring that only alphanumeric characters and safe path separators are accepted. Additionally, implementing strict allow-lists for permitted file extensions and using canonical path resolution before accessing files helps neutralize these traversal attempts effectively.