CVE-2017-16211 in lessindex
Summary
by MITRE
lessindex is a static file server. lessindex is vulnerable to a directory traversal issue, giving an attacker access to the filesystem by placing "../" in the url.
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Analysis
by VulDB Data Team • 02/16/2020
The vulnerability identified as CVE-2017-16211 affects lessindex, a static file server implementation that serves files from a specified directory. This particular weakness represents a classic directory traversal attack vector that allows remote attackers to access files outside the intended directory structure. The flaw exists in how the application processes URL parameters, specifically failing to properly validate or sanitize input containing relative path references.
The technical implementation of this vulnerability stems from insufficient input validation within the lessindex application's file serving mechanism. When a user submits a URL containing directory traversal sequences such as "../", the application does not adequately sanitize these inputs before resolving file paths. This allows an attacker to navigate up the directory hierarchy and access files that should remain restricted. The vulnerability directly maps to CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. The flaw operates at the application layer where user-supplied input is processed without proper sanitization, creating an opportunity for unauthorized file access.
The operational impact of this vulnerability is significant as it provides attackers with the ability to access any file on the server's filesystem that the application process has permissions to read. This could include sensitive configuration files, database files, source code repositories, or other confidential data stored on the system. Attackers could potentially escalate their access by traversing directories to reach system files, log files, or other sensitive resources that should remain isolated from public access. The vulnerability is particularly dangerous in environments where the static file server application runs with elevated privileges or where sensitive data is stored in accessible locations.
Mitigation strategies for this vulnerability should focus on implementing proper input validation and sanitization mechanisms within the lessindex application. The most effective approach involves normalizing all user input paths to prevent directory traversal sequences from being processed. This includes implementing strict path validation that rejects or removes any occurrence of "../" or similar traversal patterns. Additionally, the application should enforce a chroot-like mechanism that restricts file access to a predetermined directory and its subdirectories. Organizations should also consider implementing proper access controls and privilege separation to limit what files the application can access even if traversal attacks were to succeed. The remediation aligns with ATT&CK technique T1083, which covers directory and file system discovery, as this vulnerability enables attackers to perform unauthorized file system exploration. Security configurations should also include monitoring for unusual access patterns that might indicate attempted traversal attacks, and implementing web application firewalls that can detect and block such malicious requests.