CVE-2017-16123 in welcomyzt
Summary
by MITRE
welcomyzt is a simple file server. welcomyzt 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 welcomyzt file server vulnerability represents a critical directory traversal flaw that fundamentally compromises the security boundaries of the application. This vulnerability allows attackers to access arbitrary files on the server by manipulating URL parameters through the use of directory traversal sequences such as "../". The flaw stems from insufficient input validation and sanitization within the application's file handling mechanisms, creating an exploitable path traversal condition that directly violates fundamental security principles of access control and privilege separation. Such vulnerabilities are categorized under CWE-22, which specifically addresses Improper Limitation of a Pathname to a Restricted Directory, making this issue particularly dangerous as it provides unrestricted access to the underlying filesystem.
The technical implementation of this vulnerability occurs when the application fails to properly validate or sanitize user-supplied input that is used to construct file paths. When a user submits a URL containing "../" sequences, the application processes these characters without adequate filtering, allowing them to navigate upward through the directory structure. This enables attackers to access files that should remain protected within the server's restricted directories, potentially exposing sensitive data including configuration files, user credentials, application source code, and other confidential information. The impact extends beyond simple data theft as attackers can potentially execute malicious code or cause system disruption through the manipulation of critical system files.
The operational consequences of this vulnerability are severe and multifaceted, affecting both the confidentiality and integrity of the affected system. An attacker with successful exploitation can gain access to sensitive information that may include database credentials, application configuration files, user personal data, and system logs. The vulnerability also provides potential for privilege escalation attacks, as attackers might access files with elevated permissions or system-level configurations. According to ATT&CK framework category T1083, this vulnerability directly enables reconnaissance activities by allowing threat actors to enumerate the file system structure and identify valuable targets. The impact is particularly concerning in environments where the file server hosts sensitive corporate data or personal information, as it can lead to compliance violations and significant financial and reputational damage.
Mitigation strategies for this vulnerability should focus on implementing robust input validation and sanitization mechanisms at multiple levels. The primary defense involves implementing strict path validation that rejects or removes directory traversal sequences from user input before processing. This approach aligns with security best practices outlined in the OWASP Top Ten and follows the principle of least privilege by ensuring that file access operations are properly constrained. Organizations should also implement proper access controls and file system permissions to limit the impact even if traversal attempts succeed. Additionally, regular security testing including penetration testing and code reviews should be conducted to identify similar vulnerabilities in other applications. The remediation process should include implementing proper URL encoding and decoding mechanisms, using secure file access libraries, and establishing comprehensive logging and monitoring to detect suspicious access patterns. These measures collectively address the root causes of the vulnerability and provide defense-in-depth protection against similar traversal attacks.