CVE-2017-16191 in cypserver
Summary
by MITRE
cypserver is a static file server. cypserver 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-2017-16191 affects cypserver, a static file server implementation that serves files from a specified directory. This particular flaw represents a classic directory traversal attack vector that allows unauthorized access to the underlying filesystem. The vulnerability arises from insufficient input validation and sanitization within the server's URL handling mechanism, creating an opportunity for malicious actors to navigate beyond the intended document root directory. Such directory traversal vulnerabilities are particularly dangerous because they can expose sensitive system files, configuration data, and potentially user information stored on the server. The issue manifests when the application fails to properly process or sanitize URL parameters containing sequences like "../" that are commonly used to navigate up directory levels in file systems.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious URL containing directory traversal sequences such as "../" or "%2e%2e%2f" which get interpreted by the server as commands to traverse upward in the directory structure. This allows the attacker to access files that should normally be restricted to authorized users only, potentially including system configuration files, database files, application source code, or other sensitive data. The vulnerability directly maps to CWE-22 - Improper Limitation of a Pathname to a Restricted Directory, which is a well-documented weakness in software applications that fail to properly validate file paths. This weakness is classified as a path traversal vulnerability and is often categorized under the broader family of injection flaws that can lead to unauthorized access and data exposure.
The operational impact of CVE-2017-16191 is significant and multifaceted, as it can lead to complete system compromise depending on the server's configuration and the files accessible through the traversal. An attacker can potentially access sensitive system information, application source code, user credentials, and configuration files that may contain database connection strings or other privileged information. This vulnerability also aligns with several ATT&CK techniques including T1083 - File and Directory Discovery and T1005 - Data from Local System, as it enables adversaries to enumerate and extract files from the compromised system. The vulnerability can be exploited by any user with access to the server's network, making it particularly dangerous in environments where the server is publicly accessible or where network segmentation is not properly implemented. Additionally, the vulnerability may facilitate further attacks such as privilege escalation or lateral movement within the network.
Mitigation strategies for CVE-2017-16191 should focus on implementing robust input validation and sanitization mechanisms within the application. The most effective approach involves implementing proper path validation that rejects or removes directory traversal sequences from user-supplied input before processing. This can be achieved through various methods including canonicalizing file paths, implementing strict access controls, and using secure file handling libraries that automatically prevent path traversal attempts. Organizations should also consider implementing web application firewalls that can detect and block suspicious URL patterns, along with regular security audits and penetration testing to identify similar vulnerabilities in other applications. Additionally, implementing principle of least privilege access controls and ensuring that the server runs with minimal required permissions can help limit the potential damage from successful exploitation attempts. The vulnerability also underscores the importance of keeping software components up to date with security patches, as this issue was resolved in subsequent versions of the affected software.