CVE-2017-16109 in easyquick
Summary
by MITRE
easyquick is a simple web server. easyquick is vulnerable to a directory traversal issue, giving an attacker access to the filesystem by placing "../" in the url. Access is constrained, however, to supported file types. Requesting a file such as /etc/passwd returns a "not supported" error.
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Analysis
by VulDB Data Team • 02/15/2020
The CVE-2017-16109 vulnerability affects easyquick, a lightweight web server implementation that suffers from a classic directory traversal flaw. This vulnerability stems from inadequate input validation within the web server's file handling mechanism, allowing remote attackers to access arbitrary files on the underlying filesystem through crafted URL requests. The flaw specifically manifests when the application processes user-supplied paths containing directory traversal sequences such as "../" which should normally be restricted or sanitized. This represents a fundamental security weakness in the application's path resolution logic and constitutes a direct violation of secure coding practices for web applications.
The technical exploitation of this vulnerability follows a predictable pattern where an attacker crafts malicious URLs containing directory traversal sequences to navigate beyond the intended web root directory. While the vulnerability does provide access to the filesystem, it operates under specific constraints that limit the scope of accessible files. The system implements content type restrictions that prevent direct access to sensitive files like /etc/passwd, which would otherwise be accessible through the traversal mechanism. This filtering mechanism, while providing some mitigation, does not address the core vulnerability and still allows access to other file types that may contain sensitive information or system data. 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 operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the capability to access various file types that may contain configuration data, application source code, user credentials, or other sensitive information. Although access is limited to supported file types, the potential for data exposure remains significant, particularly in environments where the web server hosts applications with configuration files that may contain database credentials, API keys, or other sensitive parameters. Attackers can leverage this vulnerability to enumerate the filesystem structure and identify potentially vulnerable files or directories that could provide further attack vectors. The impact is particularly concerning in containerized environments or systems where the web server runs with elevated privileges, as it could potentially expose system-level files or application data that should remain protected.
Mitigation strategies for CVE-2017-16109 should focus on implementing robust input validation and sanitization mechanisms within the web server's path resolution logic. The most effective approach involves implementing strict path validation that rejects any input containing directory traversal sequences or that attempts to access paths outside of the designated web root. Security controls should include normalization of file paths, enforcement of access controls, and implementation of a whitelist approach for supported file types. Organizations should also consider implementing web application firewalls that can detect and block suspicious path traversal patterns. Additionally, regular security assessments and code reviews should be conducted to identify similar vulnerabilities in other applications and systems. The implementation of these controls aligns with ATT&CK technique T1083, which covers discovery of file and directory permissions, and addresses the broader category of privilege escalation through information gathering. System administrators should also ensure that the web server is configured to run with minimal required privileges and that file access controls are properly implemented to prevent unauthorized access even if path traversal attacks are successful.