CVE-2017-16222 in elding
Summary
by MITRE
elding is a simple web server. elding is vulnerable to a directory traversal issue, allowing an attacker to access the filesystem by placing "../" in the url. The files accessible, however, are limited to files with a file extension. Sending a GET request to /../../../etc/passwd, for example, will return a 404 on etc/passwd/index.js.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 06/07/2018
The elding web server vulnerability represents a critical directory traversal flaw that exposes fundamental security weaknesses in web application design and input validation. This vulnerability specifically affects the elding simple web server implementation, which fails to properly sanitize user-supplied URL paths before processing file requests. The flaw allows malicious actors to manipulate file paths through the use of relative path traversal sequences such as "../" to navigate outside the intended document root directory. This type of vulnerability falls under the CWE-22 category known as "Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')" which is one of the most commonly exploited security flaws in web applications. The vulnerability manifests when the server processes requests containing directory traversal sequences without adequate validation or sanitization of the input parameters.
The technical execution of this vulnerability demonstrates how insufficient input validation leads to unauthorized file system access. When an attacker sends a GET request with a path traversal sequence like /../../../etc/passwd, the web server attempts to resolve the requested path without proper boundary checks. The system's response reveals that it only serves files with specific extensions, suggesting that the server implements some form of file extension validation or content-type checking. However, this protection mechanism is insufficient to prevent the traversal attack, as demonstrated by the 404 error returned when attempting to access sensitive system files like /etc/passwd. This behavior indicates that while the server may filter certain file types, it does not properly validate the overall path structure, allowing attackers to bypass access controls through strategic path manipulation.
The operational impact of this vulnerability extends beyond simple file access and represents a significant risk to system confidentiality and integrity. Attackers can potentially access sensitive configuration files, system user databases, application source code, and other critical data stored on the server. The limitation to files with extensions suggests that the server may be using a whitelist approach for file types, but this protection is easily circumvented through path traversal techniques. This vulnerability aligns with ATT&CK technique T1083, "File and Directory Discovery," and can be leveraged as part of broader reconnaissance activities. The fact that the server returns a 404 error for certain paths indicates that the system has some level of access control or file validation, but this mechanism is insufficiently robust to prevent traversal attacks. The vulnerability essentially allows attackers to enumerate and access files that should remain protected within the server's restricted file system hierarchy.
Mitigation strategies for this vulnerability require implementing robust input validation and path sanitization mechanisms. The primary solution involves implementing proper path validation that strips or rejects directory traversal sequences before processing file requests. This can be achieved through various methods including canonicalization of file paths, implementing strict access controls that prevent access to sensitive system directories, and using secure file access libraries that properly handle path resolution. Organizations should implement a whitelist approach for acceptable file types and paths, ensuring that all user-supplied input is validated against a known set of safe patterns. Additionally, the server should be configured with appropriate file system permissions that prevent access to sensitive directories regardless of URL manipulation attempts. The vulnerability highlights the importance of defense-in-depth strategies and proper security coding practices, as outlined in OWASP Top Ten and NIST cybersecurity frameworks. Regular security testing including automated vulnerability scanning and manual penetration testing should be conducted to identify similar path traversal vulnerabilities in web applications and ensure that input validation mechanisms remain effective against evolving attack techniques.