CVE-2017-16209 in enserver
Summary
by MITRE
enserver is a simple web server. enserver 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-2017-16209 affects enserver, a lightweight web server implementation that suffers from a critical directory traversal flaw. This issue stems from inadequate input validation within the server's URL processing mechanism, allowing malicious actors to manipulate file paths through crafted requests containing relative path navigation sequences. The vulnerability manifests when the server fails to properly sanitize or canonicalize user-supplied URL parameters, enabling unauthorized access to arbitrary files on the underlying filesystem. This represents a fundamental security weakness in the server's file access control implementation.
The technical exploitation of this vulnerability follows the classic directory traversal pattern where attackers append sequences such as "../" to manipulate the server's file resolution process. When processed without proper validation, these sequences can navigate beyond the intended document root directory, potentially accessing sensitive system files, configuration data, or other resources that should remain protected from remote access. The flaw directly maps to CWE-22, which defines improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. This weakness allows attackers to bypass normal access controls and retrieve files that are not intended to be publicly accessible.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the ability to access critical system components including configuration files, database credentials, application source code, and potentially system binaries. An attacker could leverage this vulnerability to escalate privileges, gain persistent access to the system, or extract sensitive data that could be used for further exploitation. The vulnerability also aligns with ATT&CK technique T1083, which covers directory and file permissions enumeration, as the attacker can systematically explore the filesystem to identify valuable targets. Additionally, this weakness could enable other attack vectors such as command execution if the server is configured to execute scripts or if sensitive files contain executable content.
Mitigation strategies for this vulnerability should focus on implementing robust input validation and sanitization mechanisms within the enserver application. The most effective approach involves normalizing all user-supplied paths through canonicalization processes that resolve relative paths and prevent traversal sequences from affecting the final file resolution. Organizations should also implement proper access controls that restrict file system access to only necessary directories, utilize secure coding practices that validate all input parameters, and consider implementing web application firewalls or other protective measures. The vulnerability demonstrates the critical importance of proper input validation in web applications and highlights the need for security-conscious development practices that prevent common attack patterns from being exploited in production systems.